Abstract: The effects of phase difference between the two pulsed arcs on the arc stability and weld quality of tandem P-GMAW were investigated by using a synchronization acquisition system of images and electrical parameters. The results show that when welding at a phase difference of 0, the two peak arcs attract each other and combins into one,and the two base arcs don't affect each other. The welding process is stable without any arc interruption, resulting in good weld appearance. As the phase difference increases, arc interruption frequencies of both leading and trailing arcs increase and the weld width become uneven. When the phase difference is increased to 180°,the base arc is attracted strongly by the peak arc, and a curved bridge is formed between two wires. The base arc is elongated significantly and susceptible to extinguish, thus the arc interruption frequency reaches the maximum value. The repeated arc re-ignition causes heavy spatter and worse weld appearance.