The numerical simulation of Fire II radiation in-flight measurements is carried out. The freestream conditions at four trajectory points during Fire II re-entry are selected for the calculation. The Navier-Stokes equations in the axisymmetric form with thermochemical nonequilibrium are solved. The wall is assumed to be isothermal and fully catalytic. The radiation heat flux is estimated with an assumption of local thermodynamic equilibrium (LTE). The stagnation radiative heat fluxes are calculated in the two wavelength regions (1) 0.3-0.6 μm and (2) 0.2-4 μm. The obtained heat fluxes are slightly lower than those of the flight data through all the trajectory points.