Sea fog, as an important factor affecting the transmittance of the atmosphere, reduces the contrast between the ship targets and the sea-surface background in the infrared detection of ship targets on the sea. The traditional detection method based on infrared intensity cannot obtain ship targets as the contrast is less than the detection threshold with the increase of sea fog concentration. In view of the above situations, a background radiation suppression method based on sea surface polarimetric characteristics was developed to enhance the contrast according to the polarimetric characteristics of the sea fog scene. First, the relationship between the atmospheric transmittance of sea fog and infrared thermal radiation under different conditions is analyzed. Then, by analyzing the polarization characteristics of the sea surface radiation, a numerical model of the scene based on polarization contrast and intensity contrast was established. Finally, Analyzing the change regulation of threshold transmittance (τth) and contrast improvement (INC) under the circumstances of different detection angles, detection heights, and temperature differences between ship targets and sea surface. The simulation results indicate that INC gradually increases with the temperature difference and the detection angle decrease, along with the difference between the intensity τth and the polarization τth. but the intensity τth is always greater than the polarization τth. Therefore, the method provides a useful reference for ship detection in the sea fog environment with low atmospheric transmittance.