As the changed temperature of truss structure in a long focus camera will effect the image quality of an optical system, this paper explores the thermal design of supporting truss of the camera. First, the absorbed heat flux and heating powers of a truss rod were analyzed based on the temperature limit requirement of the optical system and the orbital parameters of the satellite. According to the analysis of thermal balance equation, it points out that the temperature difference of the truss is mainly determined by the heating power and arrangement of the heaters. Then, through the theoretical analysis of a simplified mathematical model of the truss, the temperature difference equation of supporting truss was derived, and two thermal control methods including increasing heater areas or increasing the effective thermal conductivity of the truss were presented. A new kind of material named Pyrolytic Graphite Sheet(PGS) was proved to be a candidate that can well satisfy the design requirements of increasing thermal conductivity and lighting the weight of supporting truss. On the calculation,it shows that the temperature difference has decreased from 7.9℃ to 0.83℃ with the mass of each truss increasing only 12 g by using 0.076 mm thick PGS. Finally, through the thermal vacuum test and temperature difference measurement test, it demonstrates that the analysis and simulation is valid and the PGS can withstand vacuum and temperature changes under the test conditions. The method presented in this paper is practical and effective.