In this paper, through specific description of the concept of virtual private network VPN, operating principles and the IPSec protocol, and using the OPNET software for performance simulation of IPSec VPN network, we get the result of IPSec VPN throughput of the network, which is unstable. o though IPSec VPN has improved the safety performance of data transmission, it at the same time affects the transmission efficiency. By analyzing the problems of IPSec VPN, in terms of improving safety performance, the combination of PKI and IPSec VPN program was proposed. Theoretical analysis shows that such program can indeed solve the problem of authentication imperfect, thus improving the safety performance of the network.