Abstract: The indoor wet dry alternating cycle test is conducted to simulate the atmospheric environment of marine industry on the object weathering steel Q500NH and contrast steel Q355, and the corrosion weight losses, microstructures, and electrochemical behaviors of Q500NH and Q355 steels are studied by XRD, SEM, EDS, and electrochemical workstation. The results show that as the simulation acceleration test time increases, the corrosion rate of weathering steel Q500NH decreases continuously and is significantly lower than that of Q355 steel. The thickness of the rust layer on Q500NH steel increases with the increase of corrosion time. After 192 hours of corrosion of Q500NH steel, the gap between the rust layers increases, and the corrosion products form an obvious internal and external rust layer structure. SO₄^2- and Cl^- in the marine industrial atmospheric environment continuously participate in the reaction. The corrosion products of Q500NH steel in the early stage of corrosion are mainly chemically active γ-FeOOH. With the increase of corrosion time, γ-FeOOH gradually transforms into chemically stable α-FeOOH. Compared with Q355 steel, Q500NH steel has higher polarization resistance and charge transfer resistance, which indicates that it has better corrosion resistance.