Abstract： Common cause failures(CCF) is not easy to be identified and evaluated in automatic train control(ATC) system design and development. The analysis of the failure characteristics of ATC system failures, system modelling and calculation demonstrated that CCF had a significant impact on the safety of the system. A CCF vulnerability factor was designed according to the system safety theory and the characteristics of the ATC system. Then, the process for CCF identification and screening was discussed. Based on the 2 out of 3 ATC safety architecture, the system failure probability which takes account of CCF was computed. It is found out that it is difficult to quantitatively calculate the CCF due to the lack of historical CCF data. Finally, the general CCF control measures was discussed and summarized.