:set fo=r
详情见
http://vimdoc.sourceforge.net/htmldoc/change.html#fo-table
You can use the 'formatoptions' option to influence how Vim formats text.
'formatoptions' is a string that can contain any of the letters below. The
default setting is "tcq". You can separate the option letters with commas for
readability.
letter meaning when present in 'formatoptions'
...
r Automatically insert the current comment leader after hitting
<Enter> in Insert mode.