In order to study the variation of mechanical properties of steel under different corrosion rates, the neutral salt spray corrosion test and uniaxial tensile test of 38 steel samples in 12 groups were carried out with Q235, Q355 and Q460 steel as the research objects. The degradation law of steel properties was summarized, and the prediction formula of steel strength after corrosion suitable for different strength grades was proposed. Based on the proposed prediction formula of steel strength after corrosion and the actual wall thickness after corrosion, a finite element model was established. Based on the comparison and verification with the experimental results, the influence of corrosion rate, concrete strength and slenderness ratio on the bearing capacity was analyzed, and the bearing capacity formula was predicted by different calculation methods according to different specifications. The results show that with the increase of corrosion rate, the elastic modulus of steel remains basically unchanged, and the yield platform gradually shortens or even disappears. The peak load decline rate of square section members is slightly larger than that of circular section members. The higher the concrete strength grade, the smaller the decrease of peak load after corrosion. With the increase of slenderness ratio, the increase rate of peak displacement of square section members after corrosion is slightly larger than that of circular section members. The prediction of bearing capacity by using the method of steel strength reduction combined with wall thickness reduction is more accurate and less discrete.