Abstract: Al-10Sr as the inoculant of the nugget was added into a inoculation pit to investigate the effect of Sr additive amount on the microstructure and mechanical properties of resistance spot welded magnesium alloy. Results show that when the additive amount of Al-10Sr increased from 0 to 1.4 mg, the average width of cellular dendritic crystal zone decreased from 332 μm to 58 μm, the microstructure refined obviously.The tensile shear load of the joints increased by 24.3% from 2.379 kN to 2.959 kN.