Abstract: Ni-based alloy 690 was deposited on the surface of stainless steel 347 by using TIG surfacing procedure, while electrochemical corrosion properties of the substrate stainless steel 347, surfacing layer alloy 690 and the welded joint were analyzed by electrochemical measurement technology in a 3.5% NaCl solution at room temperature. To study the corrosion mechanism of the welded joint, the microstructure and composition were analyzed by SEM and EDS, and the surface morphology after corrosion was characterized by optical microscope. Results show that the corrosion rate of the base metal and the welded joint is respectively 8.4 times and 11.8 times of the surfacing layer, indicating that the surfacing layer Ni-based alloy 690 has the strongest corrosion resistance, followed by the base metal stainless steel 347, and the welded joint has the poorest corrosion resistance. The dilution of Cr by surfacing layer in the base metal near fusion zone of welded joint is the main reason leading to the aggravated corrosion of the substrate stainless steel 347.