Abstract: In order to explore the internal cause and mechanism of the failure of the laser welding structure of the 304stainless steel gas cabinet, OM, SEM, EDS, XRD, EBSD and the hardness test of the welded joint were adopted, and the microstructure, chemical composition, fracture morphology, phase of the joint and position near the crack, crack propagation path and crack morphology of the welded joint were studied. The results show that the structure of laser welded joint is mainly composed of austenite phase, high temperature δ ferrite, and a small amount of carbide is precipitated between austenite and ferrite in the heat affected zone near the fusion line. Stress concentration is easy to occur in the heat affected zone of S laser weld. The periodic condensation and the high content of chloride ions in the coastal atmosphere make the surface of the cabinet form a water film containing chlorine ions, which prevents the formation of stainless steel passivation film. During service, stress corrosion cracking occurs under the combined action of stress and chloride ion, and cracks expand rapidly under the action of welding residual stress, eventually leading to air leakage failure.