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.