It is a kind of resistance welding process using MF DC inverter power supply (1KHZ/2KHZ/4KHZ can be set), the power input is three-phase power frequency, the output is single-phase medium frequency, due to the increase of frequency, the welding transformer volume is greatly reduced, the welding time can be calculated in milliseconds, the welding energy is more concentrated, the welded workpiece is placed between the upper and lower electrodes, the welding current and welding time are set through the medium frequency inverter resistance welding controller, and the pressure between the electrodes is set. After the welding current and welding time are set, the pressure between the electrodes is set, and when the high current passes through the welded part, the high temperature generated by the contact resistance melts the welded base material and forms the weld nucleus, which can greatly reduce the demand of the power grid compared to the AC single-phase welding power source.