The battery energy storage system (BESS) has fast response speed and strong adjustment ability, and can effectively cope with the randomness of renewable energy. However, as the proportion of battery energy storage increases, the impact of its failure characteristics on the power system reliability gradually increases. To this end, this paper proposes a power system operational reliability assessment method considering the failure characteristics of BESS. First, a multi-dimensional performance attenuation probability model of the BESS is established based on the general generating function and further combined with the thermal runaway failure warning probability of the BESS, an available output power model that comprehensively considers battery energy storage failure is established. Then, a load curtailment optimization model that takes the storage battery into account is constructed. Further, based on the Monte Carlo simulation method, the reliability assessment method that considers BESS failure is proposed. It can accurately consider thermal runaway failure and multi-dimensional performance attenuation failure of the BESS. Finally, the effectiveness of the method proposed in this article is verified in the IEEE RTS-79 bus system simulation.