The invention discloses a comprehensive reliability assessment method for a 500kV terminal substation. The method comprises the following steps of: S1. collecting reliability essential data of 500kV terminal substations in a certain range in a period of time, and main elements of peripheral 500kV power grid and 220kV power grid, wherein the reliability essential data comprise failure rate, average each failure recovery time, schedule overhauling rate and average each schedule overhauling time, respectively averaging the data to obtain input data for reliability assessment of each element; S2. calculating the reliability of the 500kV terminal substation and calculating the influence of 500kV terminal substation construction to the peripheral 500kV power grid, wherein the calculation of the reliability of the 500kV terminal substation comprises: S2-1, respectively calculating reliability of 500kV interconnection, 500kV terminal substation main connection and 220kV receiving end power grid; S2-2, analyzing the 500kV interconnection failure, 500kV terminal substation main connection failure and 220kV receiving end power grid failure according to the serial connection failure mode to calculate reliability index of 500kV terminal substation. A reliability model, an indicator system and a reliability calculating method of 500kV terminal substation are created to guide the construction of the 500kV terminal substation.