The corrosion of stainless steel car body parts is mainly intergranular corrosion,and the theory of chromium deficiency plays an important role in explaining the corrosion behavior of stainless steel. Combining with the composition of stainless steel and the relevant parameters in welding process,the influence of heat input on the corrosion performance of the welded joint in the narrow gap laser filler wire welding is studied. A corrosion test scheme for welded joint of stainless steel is designed,and based on the theory of chromium deficiency,its influence mechanism on the corrosion behavior of welded joints is discussed. In this paper,the 6 mm thick 301 L stainless steel plate is used as the base material and ER308L welding wire is used as the filler material. The corrosion behavior of the welded joints in narrow gap laser filler wire welding is studied when the heat input is 120 J/mm,150 J/mm and 180 J/mm,respectively. Electrochemical tests are carried out on the welded joints of narrow gap laser filler wire welding under three groups of different heat inputs. After immersion corrosion,three groups of samples are scanned by electron microscope,and the corrosion morphology is characterized and compared to conclude that the corrosion performance of the joint is best when the heat input is 150 J/mm.