The detection of ships and other sea targets is of great significance to sea surface management, national defense security, search and rescue, and other fields. Space-borne infrared remote sensing has a wide coverage, which is an effective means to achieve wide-area detection of ship targets. Affected by the diurnal cycle of the solar zenith angle, the temperature difference between the ship and the sea surface changes periodically, resulting in a thermal crossover period twice a day in the ship detection scene on the sea surface. In this paper, taking the mid-latitude summer and winter sea surface environment as an example, the 24-hour infrared radiation characteristics of the sea surface ship detection scene are established, and a multi-spectrum optimal combination scheme is proposed, which is realized by the detection of dual detection spectrum bands of 3.50 -4.10 μm and 10.25-10.75 μm day and night continuous observation with signal-to-noise ratio better than 15. The proposed dual-spectrum detection method provides technical support for the application of wide-area all-time sea surface target detection.