Objective To investigate the corrosion-resisting function of the Q235 steel in the ocean air atmosphere, and figure out the corrosion mechanism of the Q235 steel in the offshore environment. Methods Salt spray test and constant temperature and humidity test were used to study the corrosion rules of the Q235 steel at different temperatures, relative humidifies and chloride ion contents in simulated ocean air atmosphere. Surface corrosion morphology analysis, metallographic analysis and XRD component analysis were used to analyze the respective corrosion morphology and corrosion products. Results With increasing temperature, the corrosion rate of Q235 steel under the simulated ocean air environment was raised. With increasing chloride ion concentration, the corrosion rate was elevated in the initial stage and peaked when the chloride ion concentration was 1. 75% , after which the corrosion rate started to decrease. With increasing relative humidity, the corrosion rate of Q235 steel was accelerated, especially when the relative humidity was larger than 85% . In addition, in the salt spray environment, the corrosion manifestation of Q235 steel was pitting corrosion and the major corrosion products were Fe2O3 and Fe3O4. Conclusion Under the ocean air atmosphere, temperature, humidity and chloride ion content are all important factors that can lead to severe corrosion of the Q235 steel, and the major corrosion manifestation is pitting perforation. Therefore, surface protection measures for Q235 steel must be taken.