The microstructures of steel bars were studied by X-ray photoelectron spectroscopy (XPS), and the mechanism of corrosion of steel bars under the corrosion factors was elucidated. The results show that the passivation film and corrosive surface of the steel surface in the solution of the chloride-containing salt were coarser and the surface state was denser. The main corrosion productions are FeOOH and FeO. The surface of the steel immersed in the simulated carbonized solution was loose pores. The main components are FeOOH, Fe3O4 and Fe2O3. The surface of the steel bar has a large amount of yellowish brown corrosion products in the simulated carbonization and chloride salt. The surface of the corrosion products were stripped and the main components are FeOOH, Fe3O4 and FeCl3, where the content of FeOOH is as high as 60% or more. the peak value of iron is gradually increased from the simulated chloride salt solution to the carbonized solution to the combined effect of carbonation and chloride salt, the iron oxide content is increased and corrosion of steel is obviously serious.