To study the effects of corrosion on the mechanical properties of cold-formed thin-walled steel and hot-rolled steel materials, tensile tests were conducted on cold-formed thin-walled C-shaped steel that has been in service for many years in industrial environments. By using a 3D scan handheld laser scanner, the surface morphology of the corroded steel plate was obtained, and the influence of the degree of rust on its mechanical properties was discussed. Test results were compared with corroded hot-rolled steel to analyze effects of corrosion on the surface morphology, fracture form, stress-strain curve, and mechanical properties of the two steel products. Results show that the 3D roughness parameters S_a and S_q of the corroded cold-formed thin-walled steel gradually increased with the increase of the corrosion rate, and the growth rate was higher than that of the hot-rolled steel. The elastic modulus, yield strength, ultimate strength, and ultimate strain of the corroded cold-formed thin-walled steel decreased linearly with the increase of the corrosion rate, but the elongation decreased by a quadratic curve with the increase of corrosion rate. At the same depth of rust damage, the decrease rates of elastic modulus, yield strength, ultimate strength, ultimate strain, and elongation of the cold-formed thin-walled steel were greater than those of the hot-rolled steel, which proves that the influence of corrosion on the mechanical properties of cold-formed thin-walled steel is greater than that on hot-rolled steel.