In order to ensure the reliability design requirements of hybrid locomotives, the key components of the power battery system were comprehensively analyzed, and the key factors affecting its reliability were effectively identified. Firstly, based on the fault tree analysis (FTA) method, a fault tree model of the power battery system was established to arrive at the degree of impact of various factors on the safety risk of power battery system. Secondly, based on the results of FTA analysis, combined with the hierarchical analysis method, the system hierarchy model was established to calculate the key factors affecting the reliability of the power battery system. Finally, according to the reliability analysis results, the optimization scheme was put forward for the power battery system reliability design of hybrid locomotives, which provides theoretical basis and practical design guidance.