The formation of protective rust layer of atmospheric corrosion resistance was discussed for weathering steel.The rust layers of experimental steels were made by using an accelerating industrial atmospheric corrosion test of dry-wet cyclic immersion.Furthermore XRD were used to measure and analyze the rust layers.The initial corrosion processes below thin water film were observed and the changes of micro-area pH value were measured.The results are as follows:The corrosion processes of P-RE weathering steel are obviously different from those of carbon steel.The surface of P-RE weathering steel rapidly forms α-FeOOH and the micro-area pH value is above 5.4 during the initial corrosion period.While the component of the rust layer for the carbon steel is mainly Fe3O4 and the micro-area pH value is below 3.8. The formation of protective rust layer of atmospheric corrosion resistance was discussed for weathering steel. The rust layers of experimental steels were made by using an accelerating industrial atmospheric corrosion test of dry-wet cyclic immersion. Furtherrtherm XRD were used to measure and analyze the rust layers The initial corrosion processes below thin water film were observed and the changes of micro-area pH value were measured. The results are as follows: The corrosion processes of P-RE weathering steel are obviously different from those of carbon steel. The surface of P-RE weathering steel rapidly forms α-FeOOH and the micro-area pH value is above 5.4 during the initial corrosion period. Whhile the component of the rust layer for the carbon steel is mainly Fe3O4 and the micro-area pH value is below 3.8 .