In order to understand the corrosion behavior of bridge weathering steels at marine atmosphere, three type steels containing 3.5% Ni were prepared for alternate wet-dry accelerated corrosion test. Microstructures, rust layer morphologies and characteristics of bridge weathering steels with different Mn and Cu contents at different stages were studied by using optical microscope, XRD and SEM. The results show microstructures of the bridge weathering steels are composed of quasi-polygonal ferrite, acicular ferrite and granular bainite. Corrosion resistance of the steels is improved with Mn content increasing. Distributions of Ni and Mn are uniform inside rust layers, but Cu is enriched at gaps and pores in rust layers. Crystal phases are mainly composed of Fe₃O₄, γ-FeOOH and α-FeOOH in rust layers, however, the compositions are somewhat different at different stages. The formation of γ-FeOOH and α-FeOOH is closely related to the change in corrosion rate. With increasing Mn content, the formation of γ-FeOOH and α-FeOOH are accelerated and their sizes are restrained.