Abstract: The butt welding test of 304/Q345R composite plate was carried out by using TIG welding process. The filling metal of the base layer weld was J50 welding wire, and the filling metal of the transition layer weld and the cladding layer weld was ER309L welding wire. Optical microscope and EDS were used to analyze the metallographic structure of the base layer weld, the cladding layer weld and the distribution of elements near the weld of the transition layer. The tensile property and microhardness tests were carried out. The results show that the cladding layer weld is fine γ austenite and a small amount of δ ferrite. Using the ER309L wire can well control the dilution of Cr and Ni elements and the diffusion of C. The tensile strength of the welded joint meets the national standard requirement. The microhardness from the cladding plate 304 to the transition layer weld fluctuates in the range of 190-223 HV, the hardness of the transition layer weld is higher than that of the substrate Q345R.