Coolant flow rate of fuel for scramjet exceeds stoichiometric flow rate in the high flight Mach number. In order to lower the coolant flow rate of fuel and implement the matching between coolant flow rate and stoichiometric flow rate, the potential working for the cooling fuel was analyzed by exergy method. The properties of the cooling of fuel at supercritical pressures determines the quantity of exergy. The exergy was calculated according to the distribution of scramjet wall’s temperature, scramjet wall’s heat flux, and the exergy equilibrium equation was given. It is concluded that the heat of scramjet wall is 562.4 kW and the exergy is 541.3 kW when the maximum temperature of scramjet wall is 1200 K. It is also concluded that the potential working is lowered while the coolant flow rate of fuel is increased and the output temperature of fuel is increased, and the potential working is not changed when the output pressure of fuel is increased.