The thermal protection of hypersonic aircrafts in flight are under the threat of severe aerodynamic thermal problems.The active thermal protection technology through mass injections can effectively reduce the skin-friction and heat flux on the wall，and thus has become a hot topic in thermal protection research.However，the laws and differences in the effects of injection gases on the high-temperature hypersonic laminar/turbulent boundary layer flow are still unclear，and this is an urgent aerodynamic problem to be solved in active thermal protection design.This paper selects a two-dimensional flat model and adopts the shear stress transport （SST） model to conduct numerical simulation research on the heat flux and skin-friction reduction considering injection gases.The effects of three injection gases，i.e.，water vapor，carbon dioxide，and pyrolysis gas，on the high-temperature hypersonic laminar/turbulent flow are analyzed.The results show that under the pyrolysis gas injection，there are significant differences in the velocity and temperature distributions of the laminar/turbulent shock layer.Compared with no injection，the three gases all effectively reduce the velocity and temperature gradient at the turbulent boundary layer，and then reduce the skin-friction and heat flux on the wall.Compared with the other two gases，the pyrolysis gas has the most significant effects on the skin-friction and heat flux reduction.The research results also indicate that the three gases significantly increase the Reynolds stress and intensify the turbulent fluctuation.