diff --git a/src/component/visualMap/PiecewiseModel.js b/src/component/visualMap/PiecewiseModel.js
index df03ed051a..249658693f 100644
--- a/src/component/visualMap/PiecewiseModel.js
+++ b/src/component/visualMap/PiecewiseModel.js
@@ -398,25 +398,21 @@ var resetMethods = {
         thisOption.precision = precision;
         splitStep = +splitStep.toFixed(precision);
 
-        var index = 0;
-
         if (thisOption.minOpen) {
             pieceList.push({
-                index: index++,
                 interval: [-Infinity, dataExtent[0]],
                 close: [0, 0]
             });
         }
 
         for (
-            var curr = dataExtent[0], len = index + splitNumber;
-            index < len;
-            curr += splitStep
+            var index = 0, curr = dataExtent[0];
+            index < splitNumber;
+            curr += splitStep, index++
         ) {
             var max = index === splitNumber - 1 ? dataExtent[1] : (curr + splitStep);
 
             pieceList.push({
-                index: index++,
                 interval: [curr, max],
                 close: [1, 1]
             });
@@ -424,7 +420,6 @@ var resetMethods = {
 
         if (thisOption.maxOpen) {
             pieceList.push({
-                index: index++,
                 interval: [dataExtent[1], Infinity],
                 close: [0, 0]
             });
@@ -432,7 +427,8 @@ var resetMethods = {
 
         reformIntervals(pieceList);
 
-        zrUtil.each(pieceList, function (piece) {
+        zrUtil.each(pieceList, function (piece, index) {
+            piece.index = index;
             piece.text = this.formatValueText(piece.interval);
         }, this);
     },