This study investigated the corrosion behavior of Q235 carbon steel in the coastal atmospheric environment of Hainan.Through a four-year atmospheric exposure test，the corrosion kinetics，morphological evolution，and corrosion products of Q235 carbon steel were systematically analyzed.The results indicate that the corrosion rate of Q235 carbon steel in this environment increases over time，with the rust layer exhibiting no significant protective effect on the substrate.The corrosion products were predominantly composed of γ-FeOOH（lepidocrocite）.After prolonged exposure，β-FeOOH（akaganéite） and minor Fe₃O₄（magnetite） are additionally detected.This research provides critical insights into understanding the corrosion mechanisms of Q235 carbon steel in Hainan''s coastal-marine atmosphere and predicting its long-term service lifespan.