diff --git a/src/test/mergeWith.test.ts b/src/test/mergeWith.test.ts
new file mode 100644
index 00000000..c01b5654
--- /dev/null
+++ b/src/test/mergeWith.test.ts
@@ -0,0 +1,16 @@
+import { mergeWith } from '../utils/set';
+
+describe('mergeWith array merge', () => {
+  it('should keep existing array length when merging sparse updates', () => {
+    const allValues = { list: ['A', 'B', 'C', 'D'] };
+    const changedValues = { list: new Array(2) };
+    changedValues.list[1] = 'BB'; // 仅更新第 2 项，长度为 2
+
+    const merged = mergeWith([allValues, changedValues], {
+      prepareArray: current => [...(current || [])],
+    });
+
+    expect(merged.list).toEqual(['A', 'BB', 'C', 'D']);
+    expect(merged.list).toHaveLength(4);
+  });
+});
diff --git a/src/utils/set.ts b/src/utils/set.ts
index c0db65d5..7d465a56 100644
--- a/src/utils/set.ts
+++ b/src/utils/set.ts
@@ -111,7 +111,9 @@ export function mergeWith<T extends object>(
           }
 
           keys(value).forEach(key => {
-            internalMerge([...path, key], loopSet);
+            if (Object.getOwnPropertyDescriptor(value, key).enumerable) {
+              internalMerge([...path, key], loopSet);
+            }
           });
         }
       } else {