diff --git a/src/traverseFileTree.ts b/src/traverseFileTree.ts
index 06665d3..7b74c0b 100644
--- a/src/traverseFileTree.ts
+++ b/src/traverseFileTree.ts
@@ -10,30 +10,28 @@ interface InternalDataTransferItem extends DataTransferItem {
   path: string;
 }
 
-function loopFiles(item: InternalDataTransferItem, callback) {
-  const dirReader = item.createReader();
-  let fileList = [];
+const traverseFileTree = (files: InternalDataTransferItem[], callback, isAccepted) => {
+  const flattenFileList = [];
+  const progressFileList = [];
+  files.forEach(file => progressFileList.push(file.webkitGetAsEntry() as any));
+  function loopFiles(item: InternalDataTransferItem) {
+    const dirReader = item.createReader();
 
-  function sequence() {
-    dirReader.readEntries((entries: InternalDataTransferItem[]) => {
-      const entryList = Array.prototype.slice.apply(entries);
-      fileList = fileList.concat(entryList);
+    function sequence() {
+      dirReader.readEntries((entries: InternalDataTransferItem[]) => {
+        const entryList = Array.prototype.slice.apply(entries);
 
-      // Check if all the file has been viewed
-      const isFinished = !entryList.length;
+        progressFileList.push(...entryList);
+        // Check if all the file has been viewed
+        const isFinished = !entryList.length;
+        if (!isFinished) {
+          sequence();
+        }
+      });
+    }
 
-      if (isFinished) {
-        callback(fileList);
-      } else {
-        sequence();
-      }
-    });
+    sequence();
   }
-
-  sequence();
-}
-
-const traverseFileTree = (files: InternalDataTransferItem[], callback, isAccepted) => {
   // eslint-disable-next-line @typescript-eslint/naming-convention
   const _traverseFileTree = (item: InternalDataTransferItem, path?: string) => {
     if (!item) {
@@ -59,20 +57,23 @@ const traverseFileTree = (files: InternalDataTransferItem[], callback, isAccepte
               },
             });
           }
-          callback([file]);
+          flattenFileList.push(file);
         }
       });
     } else if (item.isDirectory) {
-      loopFiles(item, (entries: InternalDataTransferItem[]) => {
-        entries.forEach(entryItem => {
-          _traverseFileTree(entryItem, `${path}${item.name}/`);
-        });
-      });
+      loopFiles(item);
     }
   };
-  files.forEach(file => {
-    _traverseFileTree(file.webkitGetAsEntry() as any);
-  });
+
+  function walkFiles() {
+    let wipIndex = 0;
+    while (wipIndex < progressFileList.length) {
+      _traverseFileTree(progressFileList[wipIndex]);
+      wipIndex++;
+    }
+    callback(flattenFileList);
+  }
+  walkFiles();
 };
 
 export default traverseFileTree;
diff --git a/tests/uploader.spec.tsx b/tests/uploader.spec.tsx
index b7e060c..ba3e47d 100644
--- a/tests/uploader.spec.tsx
+++ b/tests/uploader.spec.tsx
@@ -25,7 +25,7 @@ const makeFileSystemEntry = item => {
       return {
         readEntries(handle) {
           if (!first) {
-            return [];
+            return handle([]);
           }
 
           first = false;
@@ -373,7 +373,54 @@ describe('uploader', () => {
     beforeEach(() => {
       uploader = render(<Upload {...props} />);
     });
+    it('beforeUpload should run after all children files are parsed', done => {
+      const props = { action: '/test', directory: true, accept: '.png' };
+      const mockBeforeUpload = jest.fn();
+      const beforeUpload = (file, fileList) => {
+        console.log('beforeUpload', file, fileList);
+        mockBeforeUpload(file, fileList);
+      };
+      const Test = () => {
+        return <Upload {...props} beforeUpload={beforeUpload} />;
+      };
 
+      const { container } = render(<Test />);
+      const files = {
+        name: 'foo',
+        children: [
+          {
+            name: 'bar',
+            children: [
+              {
+                name: '1.png',
+              },
+              {
+                name: '2.png',
+              },
+              {
+                name: 'rc',
+                children: [
+                  {
+                    name: '5.webp',
+                  },
+                  {
+                    name: '4.webp',
+                  },
+                ],
+              },
+            ],
+          },
+        ],
+      };
+      const input = container.querySelector('input')!;
+      fireEvent.drop(input, { dataTransfer: { items: [makeDataTransferItem(files)] } });
+      setTimeout(() => {
+        expect(mockBeforeUpload.mock.calls.length).toBe(2);
+        expect(mockBeforeUpload.mock.calls[0][1].length).toBe(2);
+        expect(mockBeforeUpload.mock.calls[1][1].length).toBe(2);
+        done();
+      }, 100);
+    });
     it('unaccepted type files to upload will not trigger onStart', done => {
       const input = uploader.container.querySelector('input')!;
       const files = {