Abstract: In order to solve the problems of the ability to tolerate of the system improving difficultly when network intrusion occurred, this paper puts forward an intrusion tolerance model based on semi-Markov. The SMP model was further optimized through analyzing the intrusion tolerance model security attributes quantitative. By using solving algorithm of SMP model parameters, the mean time was given to failure tracks of each system's state (ATOSF). Finally, the key points were found in the tolerance system by analyzing ATOSF tracks. After maintaining these key points, the network administrators enhance the availability and reliability of the system. Experiments show that the semi-Markov applied to intrusion tolerant system is feasible and effective, which has the advantage of simple.