Abstract: With the further advancement of China's strategies including the Maritime Power initiative and the Belt and Road Initiative, the demand for seawater corrosion-resistant steels for various offshore platforms continues to grow. However, the corrosion behavior of seawater corrosion-resistant steels in harsh tropical marine environments with high temperature, high humidity and high salt spray has not been fully studied. The lack of field exposure test data severely restricts their engineering application. In this work, field exposure tests in the tropical marine splash zone were carried out. Combined with scanning electron microscopy, micro-Raman spectroscopy, X-ray diffractometry and electrochemical tests, the differences in corrosion behaviors including corrosion weight loss and corrosion product composition between Al-Sn-Cr-Cu series seawater corrosion-resistant steel and Q355 low-alloy high-strength steel were investigated. The results show that obvious brownish corrosion product layers form on the surfaces of the two types of steels after four months of field exposure in the tropical marine splash zone. The corrosion products are composed of α-FeOOH, γ-FeOOH, β-FeOOH and Fe₃O₄. The enrichment of alloying elements such as Al, Cr and Cu in corrosion products makes the corrosion product layer of the seawater corrosion-resistant steel denser. By contrast, the corrosion product layer of Q355 steel is loose and porous due to its higher content of β-FeOOH. Electrochemical test results show that the corrosion product layer on the seawater corrosion-resistant steel possesses higher charge transfer resistance and lower corrosion current density, presenting better protective performance than that of Q355 steel. After the removal of the surface corrosion product layers, the pits on the seawater corrosion-resistant steel are mostly wide and shallow, while those on Q355 steel are mainly deep and narrow. Therefore, alloying with Al, Cr and Cu elements improves the corrosion resistance of seawater corrosion-resistant steel in the marine splash zone, which ensures the service safety of offshore platforms.