installed openwrt and openvpn on linksys e4200 v2, no problem to connect openvpn via PC client, can visit internet and IP changed to e4200's IP
But interesting that my android phone can't visit internet after connecting e4200's openvpn successfully, while no problem to connect other openvpn. Anything wrong?
Finally resolved this problem. my internal network is 192.168. xx.0, not default 192.168.1.0 , so ssh to edit /etc/config/openvpn, and change list push to 192.168.xx.0 instead of 192.168.1.0. now works great!!