The influence of different corrosion degree and type on the mechanical properties of steel was studied by tensile test of the standard specimen of the cold-formed thin-walled c-type purline with nine years of service in the industrial environment. By comparing the relationship between the mechanical properties, including the fracture morphology, stress strain curve and mechanical property index, and rust damage degree of damaged steel, the constitutive model of cold bending thin-walled steel was established, and the effect of corrosion on the mechanical properties of different materials was compared with the finite element analysis. The results show that the fracture form of the pitting specimen was a single fracture, and the overall corrosion was diversified: oblique breaking, arc breaking, and staircase break.Pitting specimens all showed the yield platform,the necking segment disappeared, and only when the corrosion rate reached 36.14%, the yield platform disappeared and the brittle fracture occurred. The yield, ultimate strength, elongation, ultimate strain, and modulus of elasticity decreased with the increase of corrosion degree. When the corrosion rate was 36%, the strength decreased about 40%, and the elongation decreased about 70%. The effect of total corrosion on strength was higher than that of pitting corrosion, and the effect of pitting on yield platform length and elongation was greater than that of total corrosion. The effect of rust on the mechanical properties of cold-formed materials was higher than that of hot rolled materials.