diff --git a/src/services/changeWellItemOrderBulk.js b/src/services/changeWellItemOrderBulk.js
index 757d3c7..476e1d9 100644
--- a/src/services/changeWellItemOrderBulk.js
+++ b/src/services/changeWellItemOrderBulk.js
@@ -11,6 +11,7 @@ import { handleSqlError } from '@frolog/express-api-server';
 export default async function changeWellItemOrderBulk(reqDto, user) {
     const t = await mysql.transaction();
     try {
+        // (1) ID 디코딩 및 유효성 검사
         const wellId = decodeHashId(reqDto.well_id);
         const userId = decodeHashId(user.id);
 
@@ -35,7 +36,7 @@ export default async function changeWellItemOrderBulk(reqDto, user) {
             };
         }
 
-        // (1) 우물 존재 및 권한 확인
+        // (2) 우물 존재 및 권한 확인
         const well = await Well.findByPk(wellId).catch(handleSqlError);
         if (!well) {
             await t.rollback();
@@ -46,7 +47,7 @@ export default async function changeWellItemOrderBulk(reqDto, user) {
             return { result: false, message: 'Unauthorized access.' };
         }
 
-        // (2) 전체 아이템 조회
+        // (3) 기존 우물 아이템 전체 조회
         const allItems = await WellItem.findAll({
             where: { well_id: wellId },
             order: [['order', 'ASC']],
@@ -61,51 +62,62 @@ export default async function changeWellItemOrderBulk(reqDto, user) {
             };
         }
 
-        // (3) 요청 대상 분리
+        // (4) 고정 순서 맵 구성
         const fixedMap = new Map();
-        const fixedSet = new Set();
         for (const { id, order } of changes) {
+            if (fixedMap.has(order)) {
+                await t.rollback();
+                return {
+                    result: false,
+                    message: `Duplicate order ${order} in changes.`,
+                };
+            }
             fixedMap.set(order, id);
-            fixedSet.add(id);
         }
 
-        const restItems = allItems.filter((item) => !fixedSet.has(item.id));
-        const newOrderList = Array(allItems.length);
-        let restIdx = 0;
+        // (5) 나머지 아이템 필터링
+        const fixedIds = new Set(changes.map((c) => c.id));
+        const remainingItems = allItems.filter(
+            (item) => !fixedIds.has(item.item_id),
+        );
 
-        for (let i = 0; i < newOrderList.length; i++) {
+        // (6) 순서대로 배치할 새 배열 구성
+        const totalLength = allItems.length;
+        const newOrderList = Array(totalLength);
+        let remainIdx = 0;
+
+        for (let i = 0; i < totalLength; i++) {
             const fixedId = fixedMap.get(i);
             if (fixedId != null) {
-                const item = allItems.find((item) => item.item_id === fixedId);
-                if (!item) {
+                const found = allItems.find((item) => item.item_id === fixedId);
+                if (!found) {
                     await t.rollback();
                     return {
                         result: false,
-                        message: `Item with ID ${fixedId} not found among existing items.`,
+                        message: `Item with ID ${fixedId} not found.`,
                     };
                 }
-                newOrderList[i] = item;
+                newOrderList[i] = found;
             } else {
-                if (restIdx >= restItems.length) {
+                if (remainIdx >= remainingItems.length) {
                     await t.rollback();
                     return {
                         result: false,
-                        message:
-                            'Mismatch between expected and available items.',
+                        message: 'Mismatch in remaining item distribution.',
                     };
                 }
-                newOrderList[i] = restItems[restIdx++];
+                newOrderList[i] = remainingItems[remainIdx++];
             }
         }
 
-        // (4) 실제 update 수행
+        // (7) 실제 DB 업데이트 수행
         for (let i = 0; i < newOrderList.length; i++) {
             const item = newOrderList[i];
             if (!item) {
                 await t.rollback();
                 return {
                     result: false,
-                    message: `Item missing at index ${i} in new order list.`,
+                    message: `Missing item at index ${i}.`,
                 };
             }
 
@@ -114,14 +126,15 @@ export default async function changeWellItemOrderBulk(reqDto, user) {
             }
         }
 
+        // (8) 트랜잭션 커밋
         await t.commit();
         return { result: true };
     } catch (err) {
-        console.error('[changeWellItemOrderBulk] Error occurred:', err);
+        console.error('[changeWellItemOrderBulk] Error:', err);
         await t.rollback();
         return {
             result: false,
-            message: 'Failed to reorder well items due to unexpected error.',
+            message: 'Unexpected error occurred while reordering items.',
         };
     }
 }