Abstract: In order to study the effects of porosity in different MIG welding Al-Mg alloy weld seam on the sensitivity of solidification crack, the lengths of weld seam solidification cracks in 8 welding processes were measured by using fishbone test plate, and the micro porosity in weld zone were observed. The results show that the weld seam solidification crack sensitivity of double pulse MIG welding is generally higher than that of single pulse MIG welding, but the number of weld porosities is less than that of single pulse MIG welding. The reason for the increase of weld seam solidification crack sensitivity in double pulse MIG welding is that the oscillation of double pulse current makes the porosities gather, which leads to the increase of gas pressure in the porosities and hinders the filling of low melting point liquid phase to micro hot cracks.