Abstract: In order to study the weldability of magnesium alloy AZ91,1.5mm thick AZ91 magnesium alloy was welded with YAG pulsed laser through the art and craft of one side welding with back formation.Analysis showed that the organization of the joint were mainly fine equiaxed grains,with clear fusion line,no significant heat-affected zone and fewer defects.The grain size of the joints was significantly smaller than the base material's.And because of a large number of Mg evaporation which eventually leads to a corresponding increase of Al and Zn in the welding zone,the micro-hardness of the joint was higher than that of the base material.The results show that AZ91 magnesium alloy has good weldability for YAG pulsed laser based on reasonable technological measures.