Aiming at the problem of machining data loss caused by machine power failure,a power-off protection function circuit was designed for WEDM CNC machine tools.In the circuit,CPLD was used as the control core, and the high-precision voltage monitor was used to monitor the working voltage in real time. When the power-down event was detected, the internal power-down protection function was activated, and the processing data of the power-down instant was stored in the RAM memory. After the power was recovered, the processing data in the RAM memory was read, so that the processing could be continued, and the power-down protection function was realized. Thereby, this can improve the processing efficiency and reduce the cost. Through program simulation and hardware test verification, the power-down protection function circuit can store and read the processing data, verifying the power-down protection circuit and the corresponding program.