According to the demands of a Wide Angle Aurora Imager (WAAI) for its optical system in temperature, the thermal design and related test of a high temperature transmission filter in the imager were performed. The optical-mechanical structure of the imager was introduced, especially the transmission filter component. Then, based on establishing a equation set for conducting and radiating thermal resistance, the thermal resistance and its effect factors in the overall heat transfer path from the transmission filter to optical bench were analyzed. Furthermore, the effect factors on the thermal resistance were taken as design variables and the sensitive variables on the barrel temperature were analyzed. Finally, the thermal design of the space optical system was implemented depending on the above analysis result. Experimental results indicate that the filter average temperature reach 105.8 ℃ and 138.2 ℃, respectively, the control temperature accuracy is less than ±2.5 ℃ and the temperature stability is less than 0.75℃/min under the cold and hot extreme cases. The temperature indexes of the mirrors and detector window also satisfy the design demands. It concludes that the design method based on thermal resistance and temperature sensitivity analysis could find the sensitive design variables rapidly, reduce the blindness during thermal design. Moreover, the thermal design of the space high temperature transmission filter satisfies the optical requirement and effectively maintains the temperature difference between transmission filters and mirrors.