Abstract: The 1mm thick 430 and 304 stainless steel sheets were welded by friction stir welding technology with rotational speed of 1200 r/min and the effects of welding speed on the microstructure and mechanical property of the lap joint were studied.The results show that with the increase of welding speed, the size of "hook" groove at both sides of the interface decreases and the thickness of the transition layer decreases, and the interface gradually changes from serrated structure to straight structure.All samples are fractured at the 430 stainless steel near the weld.The shear strength of the welded joint is the highest when the welding speed is 50 mm/min.The metallurgical reaction at the interface of the lap joint plays a leading role and mechanical connection plays a promoting role.