Abstract: The 317L/FH40 composite steel plate with thickness of 8 mm+48 mm is welded by cladding welding (repair welding) using the optimized process parameters, and then the post-welding heat treatment is carried out. The mechanical properties and microstructure of the joint are tested. The results show that the test results of mechanical properties of 317L/FH40 composite plate surfacing joints can meet the requirements of relevant standards and the needs of practical engineering. The microstructure analysis results show that the grain size grows in the heat affected zone of 317L cladding steel, and the microstructure changes in the heat affected zone of FH40 base steel. The results of microhardness test show that the hardness of the joint in each region has little fluctuation, but the hardness of different regions is different, increasing or decreasing in local regions. The results of intergranular corrosion test show that there is no intergranular corrosion tendency in the cladding welding seam.