diff --git a/lib/pen.js b/lib/pen.js
index 56c73c5..0d49efd 100644
--- a/lib/pen.js
+++ b/lib/pen.js
@@ -226,22 +226,20 @@ export default class Painter {
       height,
     } = this._preProcess(view);
     // 获得缩放到图片大小级别的裁减框
-    let rWidth;
-    let rHeight;
+    let rWidth = view.sWidth;
+    let rHeight = view.sHeight;
     let startX = 0;
     let startY = 0;
-    if (view.sHeight > view.sWidth) {
-      rHeight = Math.round((view.sWidth / width) * height);
-      rWidth = view.sWidth;
-    } else {
-      rWidth = Math.round((view.sHeight / height) * width);
-      rHeight = view.sHeight;
-    }
-    if (view.sWidth > rWidth) {
-      startX = Math.round((view.sWidth - rWidth) / 2);
-    }
-    if (view.sHeight > rHeight) {
+    // 绘画区域比例
+    const cp = width / height;
+    // 原图比例
+    const op = view.sWidth / view.sHeight;
+    if (cp >= op) {
+      rHeight = rWidth / cp;
       startY = Math.round((view.sHeight - rHeight) / 2);
+    } else {
+      rWidth = rHeight * cp;
+      startX = Math.round((view.sWidth - rWidth) / 2);
     }
     if (view.css && view.css.mode === 'scaleToFill') {
       this.ctx.drawImage(view.url, -(width / 2), -(height / 2), width, height);