Abstract: Direct numerical simulations of high-speed turbulent channel flows have been performed. The classic reference enthalpy method was evaluated and optimized by using the data with inflow Mach numbers of 3, 5, 6, 7, and 10. In fully developed turbulent flow, studies have shown that the classic reference enthalpy method is not applicable in high-speed channel flows. The wall heat flux predicted by the optimized reference enthalpy methods I and II are much better than the classic reference enthalpy method; moreover, the optimized reference enthalpy method II is more suitable, whose errors are within 10% compared with DNS. At the same time, the optimized reference enthalpy method II has been verified based on the experiment data of thermal environment of supersonic combustor.