diff --git a/esm/plugin/duration/index.js b/esm/plugin/duration/index.js
index a241d4b202e99c61467639a5756c586e0e50ceb7..9896d06941a0340fcde49641dfc8cb517d4ec400 100644
--- a/esm/plugin/duration/index.js
+++ b/esm/plugin/duration/index.js
@@ -1,6 +1,6 @@
 import { MILLISECONDS_A_DAY, MILLISECONDS_A_HOUR, MILLISECONDS_A_MINUTE, MILLISECONDS_A_SECOND, MILLISECONDS_A_WEEK, REGEX_FORMAT } from '../../constant';
 var MILLISECONDS_A_YEAR = MILLISECONDS_A_DAY * 365;
-var MILLISECONDS_A_MONTH = MILLISECONDS_A_YEAR / 12;
+var MILLISECONDS_A_MONTH = MILLISECONDS_A_DAY * 30;
 var durationRegex = /^(-|\+)?P(?:([-+]?[0-9,.]*)Y)?(?:([-+]?[0-9,.]*)M)?(?:([-+]?[0-9,.]*)W)?(?:([-+]?[0-9,.]*)D)?(?:T(?:([-+]?[0-9,.]*)H)?(?:([-+]?[0-9,.]*)M)?(?:([-+]?[0-9,.]*)S)?)?$/;
 var unitToMS = {
   years: MILLISECONDS_A_YEAR,
@@ -159,7 +159,6 @@ var Duration = /*#__PURE__*/function () {
 
     if (this.$d.milliseconds) {
       seconds += this.$d.milliseconds / 1000;
-      seconds = Math.round(seconds * 1000) / 1000;
     }
 
     var S = getNumberUnitFormat(seconds, 'S');
@@ -213,7 +212,7 @@ var Duration = /*#__PURE__*/function () {
       base = this.$d[pUnit];
     }
 
-    return base || 0; // a === 0 will be true on both 0 and -0
+    return base === 0 ? 0 : base; // a === 0 will be true on both 0 and -0
   };
 
   _proto.add = function add(input, unit, isSubtract) {
@@ -319,10 +318,6 @@ var Duration = /*#__PURE__*/function () {
   return Duration;
 }();
 
-var manipulateDuration = function manipulateDuration(date, duration, k) {
-  return date.add(duration.years() * k, 'y').add(duration.months() * k, 'M').add(duration.days() * k, 'd').add(duration.hours() * k, 'h').add(duration.minutes() * k, 'm').add(duration.seconds() * k, 's').add(duration.milliseconds() * k, 'ms');
-};
-
 export default (function (option, Dayjs, dayjs) {
   $d = dayjs;
   $u = dayjs().$utils();
@@ -339,18 +334,12 @@ export default (function (option, Dayjs, dayjs) {
   var oldSubtract = Dayjs.prototype.subtract;
 
   Dayjs.prototype.add = function (value, unit) {
-    if (isDuration(value)) {
-      return manipulateDuration(this, value, 1);
-    }
-
+    if (isDuration(value)) value = value.asMilliseconds();
     return oldAdd.bind(this)(value, unit);
   };
 
   Dayjs.prototype.subtract = function (value, unit) {
-    if (isDuration(value)) {
-      return manipulateDuration(this, value, -1);
-    }
-
+    if (isDuration(value)) value = value.asMilliseconds();
     return oldSubtract.bind(this)(value, unit);
   };
 });