Multiple optical payloads are integrated on an opto-electronic platform of tethered balloon for the surveillance of Expo Site of Shanghai. These optical payloads are exigent for the working temperature in order to get high quality image. Thermal models of payloads and the platform itself are built by Sinda/Fluint software. Based on the thermal model, a specific thermal design is worked out for the payload and the platform. The approach consists of both active and passive thermal control measures. It is showed that the thermal design is satisfactory by software simulation.