I used to use \"+y to copy text to system\'s clipboard, but it doesn\'t work in vim of Bash on Windows.
vmap y :w !clip.exe
"---------------------- :w !clip.exe
" The core command, thanks to Mitchell's answer.
"----------------------------------
" The first closes the command;
" the second suppresses "Press ENTER or type command to continue".
"--- :h map-silent
" This fix the flicker caused by external commands and .
"------------ :h leader
" `:echo mapleader` to view your leader key.
Standing on the shoulders of giants, I'm using the above solution now.