Abstract: In the present study, the validity of binary scaling parameterρ∞L in nonequilibrium flow isnumerically investigated with the charactristic time of chemicalreactions similarity, thermochemical state of the flowfield, radiationtransfer equation and similarity law for hypersonic flowfield. Thenumerical results show that the nonequilibrium dissociation process isdominant in the noqequilibrium region of the flowfield when theparameter ofρ∞L is below itscritical value. Therefore, it is validated that the parameter ofρ∞L can be applied in the simulationof the nondimensional variable distributions, wall heat transfer andionization properties in the whole flow field, and molecular radiationintensity at the stagnation point. In addition, the effectsof free stream velocities, the corresponding variables and flow regionson the validity ofρ∞L are also discussed.