A new type of variable polarity welding power modulated with high-frequency pulse current is developed.Series of high-frequency pulse current is superimposed on direct-current-electrode-negative (DCEN), which can improve the crystallization process in the weld bead as a result of the electromagnetic force generated by pulse current.Digital signal processor (DSP) is used to realize the closed-loop control of the first inverter, variable polarity output of the second inverter and high-frequency pulse current superposition.