A unified power flow controller reliability modeling and access power grid reliability assessment method is disclosed The method is started from a UPFC physical structure, and a function characteristic of a component and a logic relation are analyzed. A UPFC is decomposed into 5 subsystems, a reliability model of each subsystem is established and a series-parallel analysis method is finally used to acquire a reliability model and a reliability parameter of a UPFC apparatus. Based on that, an influence of the UPFC after being accessed n a power grid busbar voltage and a line power flow is analyzed, a voltage out-of-limit shedding load and a line power flow out-of-limit shedding load are calculated and eliminated and a power grid reliability assessment method considering the UPFC is provided. The method can be applied to a power grid planning and operation phase and has an important meaning for analyzing an influence of novel equipment on power grid reliability and then guiding later upgrading and reconstruction of a power grid.