diff --git a/simple-mind-map/src/plugins/TouchEvent.js b/simple-mind-map/src/plugins/TouchEvent.js
index 1c91f100..e2a3a741 100644
--- a/simple-mind-map/src/plugins/TouchEvent.js
+++ b/simple-mind-map/src/plugins/TouchEvent.js
@@ -78,7 +78,7 @@ class TouchEvent {
         return
       }
       const viewBefore = this.touchStartScaleView
-      const scale = viewBefore.scale * (distance / viewBefore.distance)
+      let scale = viewBefore.scale * (distance / viewBefore.distance)
       if (Math.abs(distance - viewBefore.distance) <= 10) {
         scale = viewBefore.scale
       }