Abstract: Common mode failure is a special fault that exists in the redundant structure system, which brings great safety risk to the system. In order to ensure the high safety and high stability of the train operation control system, the safe computer platform adopts heterogeneous redundant structure. In order to discuss the influence of common mode fault on redundant system, this article established two dynamic fault tree respectively for common and heterogeneous of safe computer systems, and used Markov chain analysis method to calculate failure rate and reliability. The results showed that the improved heterogeneous safety computer could reduce the negative impact of the common mode fault on the redundant structure system.