Abstract: In order to detect the function, performance and reliability of active thermal control system of a space camera, a simulation testing system to detect the active thermal control system was designed. The thermal-net mathematical model to calculate the temperature field of camera was established based on the basic law of heat transfer, orbital theory of spacecraft and the thermal control strategy, so that the active thermal control circuit could work in a simulated thermal space environment continuously, and the closed-loop testing of the active thermal control system could be realized. A method of two digital potentiometers in series was used to simulate the trend of temperature sensors, and the largest value of resistance achieves 100 kΩ and the measuring accuracy is 10 Ω. These results show that the simulation system meets the demands for total resistance and the rate of the resistance changes in design and achieves the simulated detection of the active thermal control circuit.