cd /etc/yum.repos.d/

mv CentOS-Base.repo CentOS-Base.repo.backup

wget http://mirrors.163.com/.help/CentOS6-Base-163.repo

mv CentOS6-Base-163.repo CentOS-Base.repo

yum clean all

注意：
wget http://mirrors.163.com/.help/CentOS6-Base-163.repo
mv CentOS6-Base-163.repo CentOS-Base.repo
更换成具体实际的镜像