diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index 6b37d36c..ff74e845 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -2,3 +2,4 @@ add_subdirectory(dnd-example)
 #add_subdirectory(test-taskbar) # Don't build
 #add_subdirectory(frameless-window) # Don't build
 add_subdirectory(animation-dci)
+add_subdirectory(single-instance-demo)
diff --git a/examples/single-instance-demo/CMakeLists.txt b/examples/single-instance-demo/CMakeLists.txt
new file mode 100644
index 00000000..824c901a
--- /dev/null
+++ b/examples/single-instance-demo/CMakeLists.txt
@@ -0,0 +1,17 @@
+find_package(Qt${QT_VERSION_MAJOR} REQUIRED COMPONENTS Widgets)
+
+set(BIN single-instance-demo)
+set(TARGET ${BIN}${DTK_VERSION_MAJOR})
+
+add_executable(${TARGET}
+    main.cpp
+)
+
+target_link_libraries(${TARGET} PRIVATE
+    Qt${QT_VERSION_MAJOR}::Widgets
+    ${LIB_NAME}
+)
+
+set_target_properties(${TARGET} PROPERTIES OUTPUT_NAME ${BIN})
+
+install(TARGETS ${TARGET} DESTINATION "${TOOL_INSTALL_DIR}")
diff --git a/examples/single-instance-demo/main.cpp b/examples/single-instance-demo/main.cpp
new file mode 100644
index 00000000..18c6876f
--- /dev/null
+++ b/examples/single-instance-demo/main.cpp
@@ -0,0 +1,55 @@
+// SPDX-FileCopyrightText: 2026 UnionTech Software Technology Co., Ltd.
+//
+// SPDX-License-Identifier: LGPL-3.0-or-later
+
+#include <QApplication>
+#include <QThread>
+#include <QTimer>
+#include <QDebug>
+#include <DGuiApplicationHelper>
+
+DGUI_USE_NAMESPACE
+
+// 演示场景：
+// 1. 实例 A 启动，成为单实例 primary
+// 2. 3 秒后 A 触发退出：aboutToQuit 发出（dtkgui 释放单实例锁和 server），
+//    但 main() 中模拟"有线程卡住"，进程继续存活 10 秒才真正退出
+// 3. 在这 10 秒内启动实例 B：
+//    - 若在 aboutToQuit 之前启动 → B 检测到 A 存活，正常退出（单实例保护）
+//    - 若在 aboutToQuit 之后启动 → B 应能成功成为新的 primary（本次修复的目标）
+
+int main(int argc, char *argv[])
+{
+    QApplication app(argc, argv);
+
+    if (!DGuiApplicationHelper::setSingleInstance("single-instance-demo")) {
+        qInfo() << "[demo] another instance is running, exit now. pid =" << app.applicationPid();
+        return 0;
+    }
+
+    qInfo() << "[demo] primary started. pid =" << app.applicationPid();
+
+    // 可通过参数控制退出前的存活时间，默认 3 秒后自动退出
+    int lifetime = 3000;
+    if (app.arguments().contains("--lifetime")) {
+        int pos = app.arguments().indexOf("--lifetime");
+        if (pos + 1 < app.arguments().size())
+            lifetime = app.arguments().at(pos + 1).toInt();
+    }
+
+    // 模拟退出阶段有线程卡住：事件循环退出后进程并不会立即结束
+    const int stuckSeconds = 10;
+    QObject::connect(&app, &QCoreApplication::aboutToQuit, &app, [stuckSeconds] {
+        qInfo() << "[demo] aboutToQuit: single instance released,"
+                << "process will stay alive for" << stuckSeconds << "s (simulating stuck thread)";
+    });
+
+    QTimer::singleShot(lifetime, &app, &QCoreApplication::quit);
+    const int ret = app.exec();
+
+    // 模拟卡住的清理逻辑阻塞进程完全退出
+    QThread::sleep(stuckSeconds);
+    qInfo() << "[demo] stuck cleanup finished, real exit now.";
+
+    return ret;
+}
diff --git a/src/kernel/dguiapplicationhelper.cpp b/src/kernel/dguiapplicationhelper.cpp
index 61bc4041..38afda7b 100644
--- a/src/kernel/dguiapplicationhelper.cpp
+++ b/src/kernel/dguiapplicationhelper.cpp
@@ -105,6 +105,39 @@ Q_LOGGING_CATEGORY(dgAppHelper, "dtk.dguihelper", QtInfoMsg)
 
 Q_GLOBAL_STATIC(QLocalServer, _d_singleServer)
 
+// 单实例锁文件，进程退出（aboutToQuit）时需提前释放，
+// 避免线程卡住导致进程未完全退出时新实例无法获取锁。
+// 文件名在 setSingleInstance 中设置（多次调用使用最后一次的 key）
+class SingleInstanceLock
+{
+public:
+    SingleInstanceLock() = default;
+    ~SingleInstanceLock()
+    {
+        unlock();
+    }
+
+    void reset(const QString &fileName)
+    {
+        unlock();
+        lock.reset(new QLockFile(fileName));
+    }
+
+    bool isNull() const { return lock.isNull(); }
+    QLockFile *data() const { return lock.data(); }
+
+    void unlock()
+    {
+        if (lock)
+            lock->unlock();
+    }
+
+private:
+    QScopedPointer<QLockFile> lock;
+};
+
+Q_GLOBAL_STATIC(SingleInstanceLock, _d_singleInstanceLock)
+
 // Protocol changelog:
 //   v1: version + pid + arguments
 //   v2: version + pid + arguments + envs (KEY=VALUE pairs, filtered by whitelist)
@@ -1550,15 +1583,18 @@ bool DGuiApplicationHelper::setSingleInstance(const QString &key, DGuiApplicatio
     }
 
     lockfile += QStringLiteral(".lock");
-    static QScopedPointer <QLockFile> lock(new QLockFile(lockfile));
     // 同一个进程多次调用本接口使用最后一次设置的 key
     // FIX dcc 使用不同的 key 两次调用 setSingleInstance 后无法启动的问题
+    if (_d_singleInstanceLock->isNull())
+        _d_singleInstanceLock->reset(lockfile);
+
+    QLockFile *lock = _d_singleInstanceLock->data();
     qint64 pid = -1;
     QString hostname, appname;
     if (lock->isLocked() && lock->getLockInfo(&pid, &hostname, &appname) && pid == getpid()) {
         qCWarning(dgAppHelper) << "call setSingleInstance again within the same process";
-        lock->unlock();
-        lock.reset(new QLockFile(lockfile));
+        _d_singleInstanceLock->reset(lockfile);
+        lock = _d_singleInstanceLock->data();
     }
 
     if (!lock->tryLock()) {
@@ -1604,6 +1640,23 @@ bool DGuiApplicationHelper::setSingleInstance(const QString &key, DGuiApplicatio
         qCDebug(dgAppHelper) << "===> listen <===" << _d_singleServer->serverName() << getpid();
     }
 
+    // 应用开始退出时提前释放单实例资源（关闭 server 并解锁锁文件），
+    // 避免有线程卡住导致进程未退出期间新实例无法启动
+    if (qApp) {
+        // Qt::UniqueConnection 对 lambda 无效，用静态标志防止重复连接
+        static bool connected = false;
+        if (!connected) {
+            connected = true;
+            QObject::connect(qApp, &QCoreApplication::aboutToQuit, qApp, [] {
+                if (_d_singleServer.exists() && _d_singleServer->isListening())
+                    _d_singleServer->close();
+                if (_d_singleInstanceLock.exists())
+                    _d_singleInstanceLock->unlock();
+                qCDebug(dgAppHelper) << "single instance released on quit.";
+            });
+        }
+    }
+
     if (new_server) {
         qCDebug(dgAppHelper) << "===> new server <===" << _d_singleServer->serverName() << getpid();
         QObject::connect(_d_singleServer, &QLocalServer::newConnection, qApp, [] {