The invention discloses a return-to-zero system and a return-to-zero method for an electric discharge machining machine tool. The system comprises an industrial personal computer, a motor driver, a motion control card, a motion module, a rotary coder, a photo-electronic switch and a motor, wherein the industrial personal computer is used for controlling the motion control card; the motion control card is connected with the motor driver, the rotary coder and the photo-electric switch respectively; the motor driver is used for controlling a shaft to move by virtue of the motor and driving the motion module; the rotary coder is used for feeding back the motion information of the shaft to the motion control card in real time; and the photo-electric switch is used for receiving signals and feeding back the signals to the motion control card. By adopting the method, high consistency of a zero position is realized; the consistency of a coordinate system of the machine tool which is repeatedly powered and powered off is guaranteed; the repeat accuracy is guaranteed; collision caused by machining or program running is prevented; damages and scrapping of work pieces and precision reduction of the machine tool are prevented, so losses caused by shutdown of the machine tool are reduced, the machine debugging cost is lowered, the cost for replacing shaft accessories and dismounting the shaft is lowered, the work efficiency is improved, the maintenance cost is lowered, and durable machining precision of the machine tool is guaranteed.