Survivability has emerged as a new phase for the development of network security technique, and quantifying survivability for network system helps to evaluate it exactly for the system in different environments. In this paper, we adopt a stochastic method called sequential Monte Carlo and try to reflect dynamic evolvement process of network survivability situation from several time sequences. The experiment results show that this method has the features of quantitative description, real-time calculation and dynamic tracking, and it is a good situation assessment solution for network survivability.