Abstract: Corrosion evolution of Mn-Cu weathering steels in a simulated industrial atmosphere environment was studied by wet/dry cyclic accelerated corrosion test and electrochemical test. The results showed that the corrosion rate increases with the wet/dry cycles in the initial stage of the test and decreases in the latter stage of the test. The corrosion rate of weathering steel is near to SPA-H steel and lower than that of 16Mn steel. In the early, the corrosion rate of fine grain weathering steel is faster than that of coarse grain, and the corrosion rate is the same in the latter. Rust layer of weathering steel is divided into outer and inner layers, and the inner rust layer is dense and mainly composed of α-FeOOH and a little of γ-Fe2O3 composition. Grain size has little effect on the composition of corrosion products. Rust layer of 16Mn steel is composed of α-FeOOH, γ-Fe2O3 and Fe3O4 composition. The corrosion resistance of Mn-Cu steel is better than 16Mn steel in the late corrosion test due to Cu action. The polarization behavior of the rusted steel showed that the corrosion product promotes the cathodic process and restrains the anodic process. Fine grain is in favor of the rapid formation of protective rust layer, and the change of corrosion potential and corrosion current of fine grain weathering steel in polarization curve is bigger.