Abstract: Resistance spot welding (RSW) of two-layer and three-layer aluminum alloy sheets was conducted under external magnetic field (EMF), and the effect of external magnetic field (EMF) on the nugget shift was investigated. The results show that the EMF improved the nugget shift of aluminum alloy resistance spot weld with unequal thickness. The effect of EMF became more obvious in the case of thickness combination in which the nugget shift was more serious. Tensile shear test was performed to investigate the joint strength with and without EMF. The results show that the EMF could improve the joint strength and meanwhile alleviate the nugget shift. Accordingly, the external magnetic field is an effective method to improve the joint strength and reduce the nugget shift of aluminum alloy resistance spot weld with unequal thickness.