Communication-based train control (CBTC) is the main method of railway signaling systems applying wireless communication to improve capacity by realizing the moving block. Due to the large adoption of Commercial Off-The-Shelf and the multiple interconnections with other service systems of railways, CBTC systems are facing increasing and severe information security challenges. However, there have been few studies highlighting the situation awareness of CBTC systems. This paper is intended to achieve the information security situation of CBTC systems quantitatively based on mass audit data, where the four dynamic features are both considered with the Gaussian Hidden Markov Model, the dynamic performance of critical equipment of CBTC systems is described. Baum-Welch algorithm is applied to obtain the optimal parameter of the model. Then, the forward algorithm is adopted to determine the probability distribution of hidden states. Moreover, we develop a method for an integrated SA value of CBTC systems based on entropy weight. The simulation results show the availability of the proposed approach.