In order to maintain the high reliability of Space Optical Remote Sensors (SORS) in a stratospheric thermal environment, the thermal-analysis for a SORS was carried out.The stratospheric environment over 25 km was described, including the atmosphere pressure, density and temperature,then a thermal analysis model was established.The convection heat transfer coefficients on the forward face, side surface and rear surface of SORS were calculated.Results show that the coefficients on the three surfaces are 5.009，8.259 and 3.33 W/(m2·K) respectively when the airship sails against the wind, and 2.609，2.959 and 1.005 W/(m2·K) respectively when the airship sails before the wind.Furthermore, the two temperature profiles in extreme conditions, the high temperature condition and the low temperature condition,were analyzed with the software of IDEAS.Experimental results demonstrate that the axial temperature difference of the SORS after thermal control has decreased from 15~2.7 ℃ and the convection heat transfer coefficients of an airship to the wind are increased with the increase of their relative speeds.It is concluded that the thermal control method is effective and obtained temperature data can provide references for the thermal distortion analysis and the selection of thermal control strategy.