Abstract: Now it was found fnat network loopholes in time and enhanced network security was very difficult.Aimed at these problems,the paper provided a method of intrusion prevent based on attack graphs.This method built network initial attack graphs by creating global network attack graphs algorithm.And we called attack graphs optimization algorithm to remove unreasonable paths in global attack graphs,so the attack graphs was simplified.Finally,by the algorithm of calculating attack graphs state node’s loss degree, webmaster optimized the network security policy.Experiments proved that this intrusion prevent method was reasonable and effective,and had simple and easy to do etc.