1. Goto http://mirrors.163.com/.help/ubuntu.html
2. Download source.list according to your ubuntu version.
3. Replace /etc/apt/sources.list.
Example: Ubuntu 11.10
deb http://mirrors.163.com/ubuntu/ oneiric main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ oneiric-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ oneiric-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ oneiric-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ oneiric-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ oneiric main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ oneiric-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ oneiric-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ oneiric-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ oneiric-backports main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ oneiric main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ oneiric-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ oneiric-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ oneiric-proposed main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ oneiric-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ oneiric main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ oneiric-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ oneiric-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ oneiric-proposed main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ oneiric-backports main restricted universe multiverse
