Abstract. 316LN austenitic stainless steel (ASS) has been used as a magnetic support structure for ITER. Pulse current as a new materials processing method, has many remarkable advantages. In this paper, the pulse current was used to treat the 316LN ASS welded metal welded by narrow gap MAG welding. The influence of different pulse current parameters on microstructures and microhardness of 316LN austenitic stainless steel weld metal was investigated. It was found that the microstructure of 316LN weld metal had a transitional trend from columnar sub-grains to equiaxed grains when the pulse current is increased to 700A. As the pulse current gradually increasing, the microhardness of weld metal first showed a constant trend, then decrease, and finally increase; with the increase of processing time, the microhardness of weld metal increased; with the increase of pressure, the microhardness of weld metal increased too.