于是在~/.vimrc中加入一行

set fileencodings=utf-8,gbk

OK.问题解决，再打开的时候就正常显示中文了。于是完整的.vimrc变成了：

set nocompatible
set number
filetype on
set history=1000
set background=dark
syntax on
set autoindent
set smartindent
set tabstop=4
set shiftwidth=4
set showmatch
set guioptions-=T
set vb t_vb=
set ruler
set nohls
set incsearch
if has("vms")
set nobackup
else
set backup
endif
set fileencodings=utf-8,gbk