Abstract: To address coupled heat transfer mechanisms in sealed cabins under high-altitude and low-pressure conditions, the effect of a high-temperature heat source on heat-sensitive components inside a spacecraft cabin was investigated. A unified multiphysics thermal model that incorporates heat conduction, thermal radiation, air conduction, and natural convection was established in ABAQUS and validated against low-pressure experiments. The three models showed consistent temperature profiles, with a maximum discrepancy among them of less than 15%. The peak temperature of the heat-sensitive material ranged from 89.2 ℃ to 102.3 ℃, meeting the safety requirement. Under low-pressure conditions, the conduction-radiation coupled model achieved the best agreement with the test data, with only 7% to 11% deviation, and its predictions fully encompassed the measured temperature rise. Sensitivity analysis revealed that the thermal conductivity of the component shell was the dominant parameter affecting temperature, whereas the specific heat capacity had negligible influence. These results confirm the accuracy and engineering applicability of the ABAQUS-based model in low-pressure environments and provide an efficient method for thermal safety assessment of spacecraft with high packing densities.