Abstract: S30403, S32101 and S32205 stainless steel structural parts for nuclear power plant pool cladding were corroded in a boric acid solution containing SO^2-₄ and Cl^- for six months. The corrosion resistance of the three stainless steel structural parts was studied comparatively and the corrosion mechanisms were analyzed. The results show that the S32205 stainless steel structural part had uniform corrosion and less surface corrosion products, indicating the corrosion degree was slight. The selective corrosion of the S32101 stainless steel structural part occurred, and deep corrosion pits appeared. Blue-green corrosion products were found in the corrosion pits. Stress corrosion cracking occurred in the S30403 stainless steel structural parts, and the crack fracture showed cleavage fracture morphology, indicating the corrosion was the most serious. The selective corrosion of ferrite phases occurred in the S32101 stainless steel structural part due to the potential differences between ferrite phase and austenite phase and the low chromium content in ferrite. The single-phase austenitic S30403 stainless steel structural part was sensitive to Cl^-, had high residual stresses, and could not form a two-phase synergy, resulting in stress corrosion cracking and fast crack propagation.