To assure the effectiveness of the optical system in an aerial camera and high image quality, thermal design was taken according to the thermal environment and the structure characteristic of the camera. Passive control methods such as thermal insulation were taken to overreach the thermal time constant and to reduce the sensitivity of the optical system to the external thermal environment. Heat transfer model and thermal resistant network model of the lens and the window unit were created, and the highest thermal leakages under extreme working conditions were analyzed and calculated. The heating power for maintaining the optical system temperature was obtained. According to the calculating results, the heating loops and heating power were designed. Steady-state and transient simulation was taken based on the thermal control methods and the work condition, and the heating powers were optimized. The steady-state temperature distributions of the lens and optical window were in the range of (20±1)℃, which indicated that the heat dissipation was well compensated. The transient results showed that the temperature of optical system was between 17.5℃~20.5℃, which met the thermal control index. Through the analysis, a theoretical warrant for reliability of optical system and optimization of thermal design was provided.