diff --git a/src/renderer/components/ui/mermaid-renderer.tsx b/src/renderer/components/ui/mermaid-renderer.tsx
index e02a7533..b49da3ae 100644
--- a/src/renderer/components/ui/mermaid-renderer.tsx
+++ b/src/renderer/components/ui/mermaid-renderer.tsx
@@ -1,4 +1,5 @@
-import { useEffect, useId, useRef, useState } from 'react';
+import { useCallback, useEffect, useId, useRef, useState } from 'react';
+import { Maximize2, Minus, Minimize2, Plus, RotateCcw, X } from 'lucide-react';
 import { cn } from '@/lib/utils';
 import { useSettingsStore } from '@/stores/settings';
 
@@ -38,12 +39,23 @@ interface MermaidRendererProps {
   className?: string;
 }
 
+const ZOOM_STEP = 0.1;
+const MIN_ZOOM = 0.1;
+
 export function MermaidRenderer({ code, className }: MermaidRendererProps) {
   const theme = useSettingsStore((s) => s.theme);
   const uniqueId = useId();
   const containerRef = useRef<HTMLDivElement>(null);
   const [svg, setSvg] = useState<string | null>(null);
   const [error, setError] = useState<string | null>(null);
+  const [zoom, setZoom] = useState(1);
+  const [pan, setPan] = useState({ x: 0, y: 0 });
+  const [isDragging, setIsDragging] = useState(false);
+  const [isFullscreen, setIsFullscreen] = useState(false);
+  const dragStartRef = useRef({ x: 0, y: 0 });
+  const panStartRef = useRef({ x: 0, y: 0 });
+  const svgContentRef = useRef<HTMLDivElement>(null);
+  const hasDraggedRef = useRef(false);
 
   const resolvedTheme =
     theme === 'system'
@@ -96,6 +108,8 @@ export function MermaidRenderer({ code, className }: MermaidRendererProps) {
         if (!cancelled) {
           setSvg(renderedSvg);
           setError(null);
+          setZoom(1);
+          setPan({ x: 0, y: 0 });
         }
       } catch (err) {
         cleanupMermaidElements();
@@ -115,6 +129,102 @@ export function MermaidRenderer({ code, className }: MermaidRendererProps) {
     };
   }, [code, mermaidTheme, uniqueId]);
 
+  const handleZoomIn = useCallback(() => {
+    setZoom((prev) => prev + ZOOM_STEP);
+  }, []);
+
+  const handleZoomOut = useCallback(() => {
+    setZoom((prev) => Math.max(prev - ZOOM_STEP, MIN_ZOOM));
+  }, []);
+
+  const handleReset = useCallback(() => {
+    setZoom(1);
+    setPan({ x: 0, y: 0 });
+  }, []);
+
+  const handleExitFullscreen = useCallback(() => {
+    setIsFullscreen(false);
+    setZoom(1);
+    setPan({ x: 0, y: 0 });
+  }, []);
+
+  // Calculate fit view: scale SVG to fit viewport while keeping aspect ratio, centered
+  const handleEnterFullscreen = useCallback(() => {
+    setIsFullscreen(true);
+    requestAnimationFrame(() => {
+      const svgEl = svgContentRef.current?.querySelector('svg');
+      if (!svgEl) return;
+
+      const contentArea = svgContentRef.current?.getBoundingClientRect();
+      if (!contentArea || !contentArea.width || !contentArea.height) return;
+
+      // Use getBBox to get the actual content bounding box
+      const svgRect = svgEl.getBoundingClientRect();
+      const padding = 24;
+      const scaleX = (contentArea.width - padding * 2) / svgRect.width;
+      const scaleY = (contentArea.height - padding * 2) / svgRect.height;
+      const fitScale = Math.min(scaleX, scaleY);
+
+      setZoom(Math.round(fitScale * 100) / 100);
+      setPan({ x: 0, y: 0 });
+    });
+  }, []);
+
+  const handleWheel = useCallback(
+    (e: React.WheelEvent) => {
+      if (!isFullscreen) return;
+      e.preventDefault();
+      const delta = e.deltaY > 0 ? -ZOOM_STEP : ZOOM_STEP;
+      setZoom((prev) => {
+        const next = Math.max(prev + delta, MIN_ZOOM);
+        return Math.round(next * 100) / 100;
+      });
+    },
+    [isFullscreen]
+  );
+
+  const handleMouseDown = useCallback(
+    (e: React.MouseEvent) => {
+      if (!isFullscreen || e.button !== 0) return;
+      setIsDragging(true);
+      hasDraggedRef.current = false;
+      dragStartRef.current = { x: e.clientX, y: e.clientY };
+      panStartRef.current = { ...pan };
+    },
+    [isFullscreen, pan]
+  );
+
+  const handleMouseMove = useCallback(
+    (e: React.MouseEvent) => {
+      if (!isDragging) return;
+      const dx = e.clientX - dragStartRef.current.x;
+      const dy = e.clientY - dragStartRef.current.y;
+      if (Math.abs(dx) > 2 || Math.abs(dy) > 2) {
+        hasDraggedRef.current = true;
+      }
+      setPan({ x: panStartRef.current.x + dx, y: panStartRef.current.y + dy });
+    },
+    [isDragging]
+  );
+
+  const handleMouseUp = useCallback(() => {
+    setIsDragging(false);
+  }, []);
+
+  const handleFullscreenContentClick = useCallback((e: React.MouseEvent) => {
+    e.stopPropagation();
+  }, []);
+
+  const handleFullscreenOverlayClick = useCallback(
+    (e: React.MouseEvent) => {
+      // Only exit if the user didn't drag (just a click on the overlay background)
+      if (!hasDraggedRef.current) {
+        handleExitFullscreen();
+      }
+    },
+    [handleExitFullscreen]
+  );
+
   if (error) {
     return (
       <div className={cn('overflow-x-auto rounded-lg border border-destructive/50', className)}>
@@ -145,15 +255,185 @@ export function MermaidRenderer({ code, className }: MermaidRendererProps) {
   }
 
   return (
-    <div
-      ref={containerRef}
-      className={cn(
-        'overflow-x-auto rounded-lg border border-border bg-muted/30 p-4',
-        '[&_svg]:mx-auto [&_svg]:max-w-full',
-        className
+    <div className={cn('relative rounded-lg border border-border bg-muted/30', className)} style={{ userSelect: 'none', WebkitUserSelect: 'none' }}>
+      <div
+        ref={containerRef}
+        className={cn(
+          'overflow-hidden',
+          isFullscreen && (isDragging ? 'cursor-grabbing' : 'cursor-grab')
+        )}
+        onWheel={handleWheel}
+        onMouseDown={handleMouseDown}
+        onMouseMove={handleMouseMove}
+        onMouseUp={handleMouseUp}
+        onMouseLeave={handleMouseUp}
+        onDoubleClick={isFullscreen ? undefined : handleEnterFullscreen}
+      >
+        <div
+          className="origin-center transition-transform duration-100 ease-out"
+          style={{ transform: `translate(${pan.x}px, ${pan.y}px) scale(${zoom})` }}
+        >
+          <div
+            className="p-4"
+            // biome-ignore lint/security/noDangerouslySetInnerHtml: mermaid SVG output
+            dangerouslySetInnerHTML={{ __html: svg }}
+          />
+        </div>
+      </div>
+
+      {/* Zoom controls */}
+      <div className="absolute bottom-2 right-2 flex items-center gap-1 rounded-md border border-border bg-background/95 p-1 shadow-sm">
+        <button
+          type="button"
+          onClick={handleZoomIn}
+          className="flex h-6 w-6 items-center justify-center rounded text-sm transition-colors hover:bg-accent hover:text-accent-foreground"
+          title="放大"
+        >
+          <Plus className="h-3.5 w-3.5" />
+        </button>
+        <button
+          type="button"
+          onClick={handleReset}
+          className="flex h-6 min-w-[2.5rem] items-center justify-center rounded text-xs transition-colors hover:bg-accent hover:text-accent-foreground"
+          title="重置缩放"
+        >
+          {Math.round(zoom * 100)}%
+        </button>
+        <button
+          type="button"
+          onClick={handleZoomOut}
+          disabled={zoom <= MIN_ZOOM}
+          className={cn(
+            'flex h-6 w-6 items-center justify-center rounded text-sm transition-colors hover:bg-accent hover:text-accent-foreground',
+            zoom <= MIN_ZOOM && 'cursor-not-allowed opacity-50'
+          )}
+          title="缩小"
+        >
+          <Minus className="h-3.5 w-3.5" />
+        </button>
+        {zoom !== 1 && (
+          <button
+            type="button"
+            onClick={handleReset}
+            className="flex h-6 w-6 items-center justify-center rounded text-sm transition-colors hover:bg-accent hover:text-accent-foreground"
+            title="适应初始大小"
+          >
+            <RotateCcw className="h-3.5 w-3.5" />
+          </button>
+        )}
+        <div className="mx-0.5 h-4 w-px bg-border" />
+        <button
+          type="button"
+          onClick={handleEnterFullscreen}
+          className="flex h-6 w-6 items-center justify-center rounded text-sm transition-colors hover:bg-accent hover:text-accent-foreground"
+          title="全屏查看"
+        >
+          <Maximize2 className="h-3.5 w-3.5" />
+        </button>
+      </div>
+
+      {/* Fullscreen overlay */}
+      {isFullscreen && (
+        <div
+          className="fixed inset-0 z-50 flex flex-col select-none bg-background"
+          onClick={handleFullscreenOverlayClick}
+        >
+          {/* Header bar */}
+          <div
+            className="flex shrink-0 items-center justify-between border-b border-border bg-muted/30 px-4 py-2"
+            onClick={(e) => e.stopPropagation()}
+          >
+            <span className="text-sm font-medium text-muted-foreground">Mermaid 预览</span>
+            <button
+              type="button"
+              onClick={handleExitFullscreen}
+              className="flex h-7 w-7 items-center justify-center rounded-md border border-border bg-background/95 text-sm transition-colors hover:bg-accent hover:text-accent-foreground"
+              title="退出全屏"
+            >
+              <X className="h-4 w-4" />
+            </button>
+          </div>
+
+          {/* Fullscreen content */}
+          <div className="relative min-h-0 flex-1">
+            <div
+              ref={svgContentRef}
+              className={cn(
+                'absolute inset-0 flex select-none items-center justify-center overflow-hidden',
+                isDragging ? 'cursor-grabbing' : 'cursor-grab'
+              )}
+              onWheel={handleWheel}
+              onMouseDown={handleMouseDown}
+              onMouseMove={handleMouseMove}
+              onMouseUp={handleMouseUp}
+              onMouseLeave={handleMouseUp}
+              onClick={handleFullscreenContentClick}
+            >
+              <div
+                className="origin-center transition-transform duration-100 ease-out"
+                style={{ transform: `translate(${pan.x}px, ${pan.y}px) scale(${zoom})` }}
+              >
+                <div
+                  className="p-4"
+                  // biome-ignore lint/security/noDangerouslySetInnerHtml: mermaid SVG output
+                  dangerouslySetInnerHTML={{ __html: svg }}
+                />
+              </div>
+            </div>
+
+            {/* Fullscreen zoom controls */}
+            <div className="absolute bottom-4 right-4 flex items-center gap-1 rounded-md border border-border bg-background/95 p-1 shadow-sm">
+              <button
+                type="button"
+                onClick={handleZoomIn}
+                className="flex h-7 w-7 items-center justify-center rounded text-sm transition-colors hover:bg-accent hover:text-accent-foreground"
+                title="放大"
+              >
+                <Plus className="h-4 w-4" />
+              </button>
+              <button
+                type="button"
+                onClick={handleReset}
+                className="flex h-7 min-w-[3rem] items-center justify-center rounded text-xs transition-colors hover:bg-accent hover:text-accent-foreground"
+                title="重置缩放"
+              >
+                {Math.round(zoom * 100)}%
+              </button>
+              <button
+                type="button"
+                onClick={handleZoomOut}
+                disabled={zoom <= MIN_ZOOM}
+                className={cn(
+                  'flex h-7 w-7 items-center justify-center rounded text-sm transition-colors hover:bg-accent hover:text-accent-foreground',
+                  zoom <= MIN_ZOOM && 'cursor-not-allowed opacity-50'
+                )}
+                title="缩小"
+              >
+                <Minus className="h-4 w-4" />
+              </button>
+              {zoom !== 1 && (
+                <button
+                  type="button"
+                  onClick={handleReset}
+                  className="flex h-7 w-7 items-center justify-center rounded text-sm transition-colors hover:bg-accent hover:text-accent-foreground"
+                  title="适应初始大小"
+                >
+                  <RotateCcw className="h-4 w-4" />
+                </button>
+              )}
+              <div className="mx-0.5 h-4 w-px bg-border" />
+              <button
+                type="button"
+                onClick={handleExitFullscreen}
+                className="flex h-7 w-7 items-center justify-center rounded text-sm transition-colors hover:bg-accent hover:text-accent-foreground"
+                title="退出全屏"
+              >
+                <Minimize2 className="h-4 w-4" />
+              </button>
+            </div>
+          </div>
+        </div>
       )}
-      // biome-ignore lint/security/noDangerouslySetInnerHtml: mermaid SVG output
-      dangerouslySetInnerHTML={{ __html: svg }}
-    />
+    </div>
   );
 }