Abstract: The satellite operates in deep space DRO orbit （Distant Retrograde Orbit）, and the on-board science payload Soft X-ray Imaging telescope （SXI） consists of a lead glass coding plate matched with a large-area CMOS. Due to the large field of view of the telescope and the high power consumption of the CMOS, the thermal environment in the DRO orbit is very complicated, while the CMOS needs to work in a low temperature environment near −30 ℃. In order to guarantee that SXI can be used reliably for a long period of time in the deep space orbit environment, a variety of thermal design schemes have been developed. In addition, finite element comparative simulations have been carried out on the temperature field under these methods: heat insulation and heat conduction mounting options, with or without heat pipes and heat sinks, and a range of thermal control measures. The installation of heat insulation for the SXI and satellite module was finalized, the connection option of CMOS components with four heat pipes to disperse internal power consumption through the heat sink was identified, and multi-layer heat-insulating components were wrapped around the outer frame and white paint sprayed on the heat-sink panels. The simulation results demonstrate that the thermal design of the SXI meets the temperature control requirements, the temperature value satisfies the thermal control index, and the thermal design is reasonable. It provides a reference for the implementation of thermal control in subsequent thermal balance tests and thermal tests of the whole satellite.