Three-dimensional morphology scanning, monotonic tensile test, and fracture scanning of cold-formed steel with 10 years of service in the industrial environment were performed to investigate the effect of corrosion on the surface morphology and mechanical properties of cold-formed steel. The two-dimensional and three-dimensional surface topography, corrosion damage parameters, stress-strain curves, mechanical property indexes, and microscopic fracture topography of the corroded cold-formed steel were obtained. The variation rules of the corrosion damage parameters and mechanical property indexes were also analyzed. Finally, a constitutive model of the corroded cold-formed steel was established. The results indicate that the number of corrosion pits on the steel surface decreased, and the morphology of corrosion pits changed significantly with the increase in corrosion degree. The proportion of the uniform corrosion and maximum depth of the corrosion pits gradually increased, and the surface of the corroded steel became increasingly rougher. The elastic modulus, yield strength, ultimate strength, and elongation after fracture linearly decreased with an increase of the material loss rate. The yield platform also became shorter or even disappeared. Moreover, the macrofracture and microfracture morphologies changed obviously. The established constitutive model can accurately reflect the variable trend of the stress-strain curve of the corroded cold-formed steel.