Abstract: This paper systematically analysis the effect of external magnetic field (EMF) on the nugget size, mechanical properties, and microstructure of aluminum alloy resistance spot welds. The results showed that the nugget diameter, tensile shear force and energy absorption were increased under the help of EMF. Under different welding parameters, the nugget diameter can be increased by 5%~25%, and the tensile shear force can be enhanced by 10%~30%. The EMF can reduce the welding current, shorten the welding time, thereby improves the welding efficiency and reduce energy consumption. The EMF promoted the formation of equiaxed crystal and refined the grain size. Besides, the study also found that both small and larger welding current and short and long welding time will reduce the effect of EMF. Accordingly, in order to maximize the effect of the EMF on resistance spot welds, reasonable welding parameters should be carried out.