The utility model discloses a stabiliser relief valve power supply unit of nuclear power plant and system is applied to reactor -cooling system's relief valve, include: the switch element switches on when the the normal power supply of relief valve power is in electric state, keep apart the unit, have two mutual isolations the input and with an output of two inputs intercommunications, the solenoid of the relay that the output of keeping apart the unit is used for corresponding with the relief valve is connected, input of isolation unit and the the normal power supply power of relief valve is connected, keeps apart another input of unit and is connected with the one end of switch element, rectifier unit, stand -by power supply is connected to rectifier unit's input, and rectifier unit's the output and the other end of switch element are connected, stand -by power supply is hydrostatic test pump turbine generator system 's alternating current power supply. The utility model discloses can realize power supply redundancy, increase the reliability of relief valve, avoid the high pressure to melt a heap occurence of failure, and owing to keep apart the existence of unit, avoid the anti - electric phenomena of sending.