Abstract: As an important part of High Speed Railway Natural Disaster and Foreign Object Invasion Monitoring System, the Foreign Object Invasion Monitoring Subsystem played an important part for the safety of high-speed-railway's operation. In this article, Fault Tree Analysis(FTA) was applied to establish the analytical models for the failure of Foreign Object Invasion Monitoring System based on the analysis of the failure factors of the Subsystem. Through analyzing the importance degree of the minimum cut sets and structure, the failure factors were sorted according to their influence level, and evaluated by FTA. The results obtained can be used for reference to improve the operation and maintenance of the Subsystem.