Abstract: In view of the fact that the requirements of the forming quality of the joint welded by dissimilar magnetic stainless steel for mechanism are higher, the high power fiber laser modulated with external magnetic pulse was used to weld the dissimilar magnetic stainless steel, and the effect of pulse modulation parameters on weld formation was studied. The results show that the morphology and size of welded bead is greatly affected by the pulse shape and frequency. The well-formed weld can be obtained by the trapezoidal wave and the pulse with frequency about 500 Hz. In addition, the pores can be suppressed by using N₂ protection in the high power fiber laser welding.