The utility model discloses a device for detecting overpressure of a circuit hydrostatic test of a pressurized water reactor nuclear power plant. The device comprises a sensing transmitter, an actuator, a box body, an input interface, a PLC and an output interface, wherein the input interface is arranged on the box body and used for inputting a detection signal output by the sensing transmitter, the PLC is arranged in the box body, electrically connected with the input interface, and used for processing the detection signal of the sensing transmitter and generating an output signal according to the processed detection signal and a preset value, and the output interface is arranged on the box body, electrically connected with the PLC and used for outputting the output signal to the actuator. According to the technical scheme, the device for detecting the overpressure of the circuit hydrostatic test of the pressurized water reactor nuclear power plant is small in size, low in weight and convenient to carry and maloperation risks do not exist.