The sharp edges of a lift body can lead to a harsh aerodynamic thermal environment, which adversely affects the structural strength of the vehicle and produces thermal strain and material ablation. To resolve this problem, an externally tangential circular extension method to blunt the lift body was proposed. Numerical simulation was employed on the configuration under blunt and no-blunt situations. Impacts of parameters on performances, including the lift-drag ratio, the maximum wall heat flux, the volume and the volume ratio were investigated through sensitivity analysis. The no-blunt shape was optimized with the objective to maximize the lift-to-drag ratio, the volume and the volume ratio. A uniform blunt method and a non-uniform blunt method were applied to the optimized shape. The effect of blunt on the aerodynamic thermal characteristics and aerodynamic performance of shapes blunted by two methods were analyzed. The results indicate that influence of design variables on performance are not altered after blunt. The enlargement of blunt radius brings out decrease of maximum wall heat flux and a reduced degree of heat flux attenuation. The uniform blunt method not only leads to leakage of high-pressure gas from windward side of the lift body to leeward side, but also gives rise to decrease in lift-drag ratio and rise in volume ratio. The non-uniform blunt method contributes to diminish loss of high-pressure gas and increase lift-drag ratio slightly. The maximum heat flux of non-uniform blunt shape is well below that of no-blunt one. Both of the two blunt methods have a significant improvement on the thermal environment.