Abstract: The reliability of power system of offshore oilfield group has a significant impact on the oil production. Considering that this kind of power system is an independent power system including generation, transmission and distribution systems, and load shedding measures are different from those of onshore power system when a fault occurs, the traditional reliability evaluation model and algorithm cannot be applied directly. A reliability evaluation method is proposed for offshore oilfield power system based on the system-wide reliability evaluation theory, and an index system is set up for the system-wide reliability. During the state sampling,the whole power system sampling can be divided into generation and transmission system sampling and distribution system sampling according to the system-wide reliability evaluation theory, and the comprehensive evaluation method can be established.In the state evaluation of generation and transmission system, the load curtailment model based on priority trip is constructed considering the characteristics of offshore power system and its load. In the state evaluation of distribution system, the effects of cascading failure are taken into consideration. Finally, evaluation is conducted on a practical example of an offshore oilfield power system. The system-wide indices are obtained and the influences of the four kinds of failures are analyzed to prove the correctness and effectiveness of the proposed method.