The corrosion behavior of A517Gr. Q steel was studied by mass loss method, SEM, EDS, XRD, and FT-IR in a cyclic wet/dry testing chamber, which was specially designed to simulate the corrosion condition of marine splash zone i.e. cyclically wetting in 3.5%NaCl solution and drying in atmospheres with humidity of either (62±5)% or (83±5)%. The results show that A517 steel is suffered from serious corrosion in the simulated environments of marine splash zone. The corrosion mass loss increases with time, while the average corrosion rate increases first and then stabilizes. The corrosion products are all composed of γ-FeOOH, β-FeOOH, α-FeOOH and Fe₃O₄. In the condition when the chamber atmosphere with humidity of 62%RH, the electrolyte film formed on the steel surface after immersion can be maintained only for a shorter period, as a result, the steel surface undergoes distinct dry and wet changes, and the formed rust scale is porous with obviously high amount of β-FeOOH, which is of high cathode oxidation activity, thus the steel presents much severe non-uniform corrosion. On the other hand, when the chamber atmosphere with humidity of 83%RH, the corrosion products scale is much dense and uniform with higher amount of Fe₃O₄, therefore, exhibits a blocking effect on the attack of aggressive Cl^- to certain extent.