In order to improve the safe level of network security, the fuzzy neutral network is applied in optimal attack and defense decision. Firstly, the theory model of attack and defense decision system for network security based on game theory is constructed, the game model of attack and defense model and the dynamical game model of incomplete information are deduced respectively. Secondly, the basic theory of fuzzy neutral network is analyzed, the framework of diagram of fuzzy neutral network is confirmed, and the model of fuzzy membership function is constructed.. Thirdly, the training algorithm of fuzzy neutral network based on improved genetic algorithm is designed, and computing method in every step is given in detail. And the Evaluation of suspicious person and system is carried out. Finally, simulation experiments are carried out, and results show that system profit and response efficiency is improved, then fuzzy neutral network can obtain higher system profit and response efficiency.