Abstract: In this paper, China low activation martensitic (CLAM) steel was welded by tungsten inert gas welding, and the corrosion properties of the welding seam in flowing liquid Pb-Bi was investigated. The result indicated that the main characteristic of corrosion was element diffusion and migration, a double layer of oxide was formed on the surface of all samples. The post weld heat treatment significantly improved the corrosion resistance of welded joints, and the tempering of 760℃/30 min presented the best performance. The homogeneous fine martensite structure effectively improved the corrosion resistance of the welded joint, and the decisive factor of the corrosion resistance was the martensite size. The failure occured in the welded area, especially the welding seam firstly. The main mechanism was the cracks growing and propagation in the inner layer, which induced the oxide layer breaking away from the matrix. Therefore, improving the corrosion resistance of the welding seam can effectively extend the service life of the materials.