Abstract: The star sensor is one of the most important parts for the attitude control and the astronomic navigation of spacecraft. For a remote-sensing satellite in orbit, it is essential to reduce the temperature fluctuations of the star sensor in order to reduce the deviation of the star sensor optical axis directing error for achieving a more precise control of the satellite’s attitude. In this paper, some conventional thermal design methods are implemented to realize the (T±2) ℃ temperature control stability for the separated active pixel sensor (APS) used on a certain sun-synchronous satellite. The thermal analysis result and the in-orbit operation data have validated the above design in meeting the temperature control requirement of the installation flange and bracket. The methods can provide a reference for the thermal design of other separated type star sensors.