在/etc/apt/sources.list靠前的地方加入即可。
说明：http://mirrors.163.com/.help/ubuntu.html
#15.10 wily, 15.04 vivid, 14.10 utopic, 14.04 trusty, 12.04 precise, 10.04 lucid deb http://mirrors.163.com/ubuntu/ wily main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ wily-security main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ wily-updates main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ wily-proposed main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ wily-backports main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ wily main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ wily-security main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ wily-updates main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ wily-proposed main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ wily-backports main restricted universe multiverse
注意注释行，列举了相应的版本源，请根据实际情况修改。