In order to discover the network vulnerability timely and solve the very serious problems of network security, this paper puts forward the attack graph which is based on intrusion detection method. The method uses the generation global network attack graph algorithm to build network initial attack graph, and call attack graph optimization algorithm to remove global attack graph unreasonable path, and achieve the goal of simply attack graph. Finally, management personnel get the basis which is computed nodes in each state attack graph algorithms degree of loss to optimize the network security. Experiments show that the intrusion detection method is reasonable and effective, and has the advantages of simple and easy.