Abstract: The chazacteiistics and mechanism of the unsteady aerodynamic heating of a transient hypersonic borurdary layer caused by sudden change in surface temperature was studied, the complete time history of wall heat flax was presented by both analytical and numerical approaches. With analytical methods, the unsteady compressible boundary layer equation was solved. In the neighborhoods of initial and final steady state, the transient response can be expressed by a steady-state solution plus a perturbation series, respectively.By patching these two solutions, the complete solution in the elrtire time domain wag achieved. In the region where the assumptions of analytical approach are satisfied, the numerical and analytical results were matched well, proving the reliability of the methods. The result showed two distinct features of the unsteady response. In the short period just after a sudden increase in the wall temperature, the direction of the wall heat flux reverted, a new inflexion near the wall arose in the profile of the thermal boundary layer, which is a typical unsteady characteristic. However, these unsteady responses only exist in a very short period in hypersonic flows, which means that, in a long-term aerodynamic heating process concidering only rinsready surface temperature, the unsteady characteristics of the flow can be ignored and the traditional quasi-steady aerodynamic heating prediction methods are still valid.