Abstract: In this paper, direct numerical simulation (DNS) studies are carried out on the hypersonic and high-enthalpy turbulent boundary layer, and the coupling mechanism of the high-temperature gas effect and turbulence is analyzed. It is found that the high-temperature gas effect significantly reduces the mean temperature and increases the mean density in boundary layer, while reduce the temperature fluctuation. In the near-wall area, both the velocity fluctuation and density fluctuation are enhanced. But in the outer area of boundary layer, these turbulent fluctuations are suppressed by high-temperature gas effect. For the Reynolds stress, high-temperature gas effect decreases the Reynolds stress value in the area of y⁺>500 in boundary layer, while increases the Reynolds stress value in the region of y⁺ < 500, which in turn enhances the momentum exchange caused by turbulence. Thereby, skin friction is increased. The wall heat transfer is strengthened by high-temperature gas effect as well. Moreover, the high temperature gas effect increases both the mean pressure and the fluctuation pressure at wall.