在/etc/apt/sources.list靠前的地方加入即可。
说明：http://mirrors.163.com/.help/ubuntu.html
#Ubuntu 15.10 wily, Ubuntu 15.04 vivid,Ubuntu 14.10 utopic,Ubuntu 14.04 trusty,Ubuntu 12.04 precise, Ubuntu 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Ubuntu版本源，请根据实际情况修改。