In this paper, the solar radiation, the earth radiation and the earth albedo radiation received by the space target are simulated by Monte Carlo simulation method, and the simulation program is written based on the unstructured tetrahedral grid, and the calculation results are compared and verified. Furthermore, for the orbit external heat flow received by the sun-synchronous orbit satellite, the grid with solar panels is used to analyze the orbit external heat flow received by each surface with or without occlusion. The results show that the average heat flow value of -Y surface decreases by 53.79 W/m² after considering occlusion in the earth-pointing mode. The average surface heat flow value of +Y-Z side panel decreased by 32.05 W/m². The temperature characteristics of each surface are given combined with the properties of surface materials, and the accuracy of the calculation is verified by combining with the on-orbit telemetry data of the solar panel temperature. Finally, the infrared radiation intensity in each direction of the two modes is calculated. The results show that the influence of heat flow on the surface is different under different observation modes. The temperature of each surface varies greatly over time in the earth-pointing mode, while the heat flow on each surface is relatively stable in the sun-pointing mode. Under both modes, the temperature of the solar panel is higher, the radiation intensity is larger, and it has obvious infrared characteristics, which facilitates infrared observation.