A method and system for evaluate that risk of simultaneous commutation failure of multiple DC circuits, A method and system for reduce that voltage coupling factor of a critical ac/dc system by calculate a voltage coupling factor of the ac/dc system and simplifying the voltage coupling factor of the critical ac/dc system, and comparing the voltage coupling action factor of the AC/DC system and thesimplified critical AC/DC voltage coupling action factor, judging whether each inverter side commutation bus of the DC system has the risk of simultaneous commutation failure according to the comparison result, the principles of the method and the system evaluation method are clear, Aiming at different AC busbars of the same HVDC system, the same simplified critical AC/DC system voltage couplingaction factor is obtained, which reduces the computational load and is convenient and fast. It is of great significance to guide the planning of large power network and to maintain the safe and stableoperation of large power network.