The work aim to study corrosion behavior of SMA490BW weathering steels for bogie welded structures and their welding joints fabricated under different welding process conditions in simulated industrial atmospheric environment. In the method of cyclic immersion corrosion test, surface morphology, rust layer structure and phase composition of corrosion products were studied by using scanning electron microscope(SEM), X ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Corrosion weight loss rate of SMA490BW weathering steel base metal, automatic MAG welding joint and manual MAG welding joint firstly increased and then decreased in simulated industrial atmospheric environment. The corrosion weight loss rate of automatic MAG welding joint was the smallest, that of the manual MAG welding joint was the largest, while that of the SMA490BW weather steel base metal fell in between. Phase composition of the weathering steel base metal and its welded joints was all γ-FeOOH, α-FeOOH, Fe2O3 and Fe3O4. After 150 h corrosion, content of Cr, Ni and Cu alloying elements in the corrosion products of the weathering steel base metal and its welding joints were different. The maximum content of Cr, Ni and Cu alloying elements in the corrosion products of automatic MAG welding seams was 1.79% 0.23%, 0.17%, respectively. Cr, Ni and Cu alloying elements would directly affect corrosion resistance of weathering steel base metal and its welding joints. Compared with the manual MAG welding joint, main reason for high corrosion resistance of automatic MAG welding joint is high content of Cr, Ni, Cu alloy elements which mainly suppress corrosion of rust layer in welding seams.