Abstract: In the current technology adopted by VPN, IPSec VPN,which has great advantage in flexibility, security, reliability and expansibility is focused, This article first analyses the architecture, the work pattern and the secure services of IPSec; and then compares the secure services it can provide when it works under different compositions of the work patterns through experiment. Finally, by combining with the involved requirements of computer classified security protection, the paper discusses the feasibility of IPSec VPN to realize these requirements.