Abstract: During sunrise, the infrared radiation difference between ship target and sea surface background is small, which increases the difficulty of target detection. To address this issue, a ship-ocean-atmosphere unsteady thermal coupling model was constructed based on FLUENT software. Combined with the Elfouhaily sea spectrum, a large-scale dynamic sea surface scene was generated, and the solar radiation, sky radiation, and atmospheric transmittance were calculated using the combined atmospheric radiative transfer (CART) software. By solving target surface temperature field and radiative transfer equation, high-precision infrared radiation characteristics of the ship in 8 μm~12 μm band were simulated, and infrared images under various observation conditions were generated.The results indicate that during nighttime, in the absence of solar irradiation and under low ambient temperature conditions, the ship hull surface temperature approaches the background temperature after prolonged exposure to the low-temperature environment throughout the night, resulting in a high degree of fusion between the target infrared signature and the sea surface. After sunrise, due to interference from environmental radiation such as sunlight and skylight scattered by the sea surface, the detectability of the ship target is significantly reduced. Nevertheless, local heat sources such as chimneys and radar panels remain conspicuously bright and serve as key features for ship target recognition.