Abstract: Based on computational fluid dynamics (CFD) technology and combined with the discrete ordinate (DO) radiation model, the surface solar radiation distribution of the electronic equipment cabin of a certain type of near space vehicle and its influence on the heat dissipation process inside the cabin are investigated. A three-dimensional thermal simulation model is established to compare and analyze the forced air cooling heat dissipation characteristics under two extreme conditions: ground high-temperature and normal-pressure (environmental temperature 45 ℃) and 20 km high-altitude low-pressure (environmental temperature −45 ℃, pressure 5.5 kPa). Numerical simulation results indicate that under normal-pressure conditions, the highest temperature inside the cabin reaches 62.82 ℃. Under low-pressure conditions, although convective heat dissipation efficiency decreases due to reduced air density, the low-temperature environment compensates for the heat load, and the highest temperature inside the cabin remains stable at 40.48 ℃. Both conditions satisfy the temperature control requirements of the equipment. Further verification is conducted through low-pressure environment simulation tests, showing that the maximum deviation between numerical calculation results and measured data is 7.9%. This confirms the reliability of the coupled radiation-convection heat dissipation analysis method. The multi-physics field joint simulation strategy proposed in this study provides theoretical support and engineering reference for the thermal management design of electronic equipment in extreme near space environments.