1、首先备份/etc/yum.repos.d/CentOS-Base.repo

mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup

2、根据CentOS版本选择操作
CentOS-5

wget http://mirrors.163.com/.help/CentOS5-Base-163.repo -O /etc/yum.repos.d/CentOS-Base.repo
yum makecache

CentOS-6

wget http://mirrors.163.com/.help/CentOS6-Base-163.repo  -O /etc/yum.repos.d/CentOS-Base.repo
yum makecache