Abstract: Based on Donnell-Mushtali approximate theory, combined with thermal elasticity theory, the axial load-bearing capability of MT300/KH420 carbon fiber/polyimide resin composite shell at ambient temperature, 420℃ and circumferential temperature distribution of 210–420℃ were evaluated by analytical methods, taking into consideration of the thermal deformation of structure, material’s degradation and other terms at high temperatures. In addition, the FEM analysis model was established by ABAQUS, which introduced the 1st buckling mode generated by buckle analysis as the original imperfection, and then studied the axial stability characteristics of MT300/KH420 composite shells by non-linear explicit dynamic method. The instability load and buckling mode are both presented which agree with the results obtained by analytical method. Furthermore, a thermal-mechanical joint axial compression test was designed and implemented, thus the failure loads and modes were obtained at above thermal fields. The results indicate that the material’s degradation and asymmetry deformation caused by non-uniform thermal fields are principal factors which impact the load-bearing capability of MT300/KH420 composite shells at high temperatures.