In order to keep the proper temperature gradient of molten pool in the process of solidification and then make the columnar crystals grow from substrate during laser metal direct forming, the liquid argon is sprayed to the two sides to refrigerate entity-wall; and the influence of liquid argon cooling on microstructure and microhardness of 316 L stainless steel parts are investigated. It can be concluded from the experiments that heat accumulation can be reduced effectively, the most of columnar crystals grow from substrate continuously, the biggest primary spacing of dendrites is about 35 μm and the microhardness of entity-wall increases obviously.