Abstract: In order to keep the welding heat input constant, number of strong and weak pulse has been changed concurrently to achieve double pulse low-frequency modulation. Based on the directly welding electrical signal waveform, indirect macro and micro metallographic, three different frequency of double pulse and one single pulse weld were compared. The results show that the stirring effect of double pulse on molten pool made the weld better than that of the single pulse. With the changing of double pulse low-frequency, the modulating frequency of 3.8 Hz was close to the weld pool oscillation frequency, by which weld pool oscillation was strengthened. The weld heat affected zone decreased, weld grain refined, and welding performance was the best.