diff --git a/src/constant.js b/src/constant.js
--- a/src/constant.js
+++ b/src/constant.js
@@ -26,5 +26,5 @@ export const FORMAT_DEFAULT = 'YYYY-MM-DDTHH:mm:ssZ'
 export const INVALID_DATE_STRING = 'Invalid Date'
 
 // regex
-export const REGEX_PARSE = /^(\d{4})-?(\d{1,2})?-?(\d{0,2})[^0-9]*(\d{1,2})?:?(\d{1,2})?:?(\d{1,2})?.?(\d{1,3})?$/
+export const REGEX_PARSE = /^(\d{4})[-/]?(\d{1,2})?[-/]?(\d{0,2})[^0-9]*(\d{1,2})?:?(\d{1,2})?:?(\d{1,2})?.?(\d{1,3})?$/
 export const REGEX_FORMAT = /\[([^\]]+)]|Y{2,4}|M{1,4}|D{1,2}|d{1,4}|H{1,2}|h{1,2}|a|A|m{1,2}|s{1,2}|Z{1,2}|SSS/g

diff --git a/test/parse.test.js b/test/parse.test.js
--- a/test/parse.test.js
+++ b/test/parse.test.js
@@ -1,6 +1,7 @@
 import moment from 'moment'
 import MockDate from 'mockdate'
 import dayjs from '../src'
+import { REGEX_PARSE } from '../src/constant'
 
 beforeEach(() => {
   MockDate.set(new Date())
@@ -125,3 +126,12 @@ it('Clone with same value', () => {
   const another = newBase.clone()
   expect(newBase.toString()).toBe(another.toString())
 })
+
+describe('REGEX_PARSE', () => {
+  it('2020/9/30', () => {
+    const date = '2020/9/30'
+    const d = date.match(REGEX_PARSE)
+    expect(dayjs(date).valueOf()).toBe(moment(date).valueOf())
+    expect(d.join('-')).toBe('2020/9/30-2020-9-30----')
+  })
+})

parseDate error from recent release.
**Describe the bug**
from https://github.com/iamkun/dayjs/pull/969
```
// v1.8.30
export var REGEX_PARSE = /^(\d{4})-?(\d{1,2})-?(\d{0,2})[^0-9]*(\d{1,2})?:?(\d{1,2})?:?(\d{1,2})?.?(\d{1,3})?$/;


// v1.8.31
export var REGEX_PARSE = /^(\d{4})-?(\d{1,2})?-?(\d{0,2})[^0-9]*(\d{1,2})?:?(\d{1,2})?:?(\d{1,2})?.?(\d{1,3})?$/;
```
result：
![image](https://user-images.githubusercontent.com/17005098/89159563-3ba04980-d5a2-11ea-9ce8-ca809da1c0c8.png)

```
// v1.8.31
dayjs('2020/9/30').format(); // result: 2020-01-01T09:00:00+08:00
```

**Expected behavior**
```
// v1.8.30
dayjs('2020/9/30').format(); // result: 2020-09-30T00:00:00+08:00
```

**Information**
 - Day.js Version [e.g. v1.8.31]


Thanks, fixed in https://github.com/iamkun/dayjs/pull/980#issuecomment-667884647
test/timezone.test.js(1) test/timezone.test.js(2) test/timezone.test.js(3) test/timezone.test.js(4)
test/parse.test.js