Abstract: Due to the thermochemical non-equilibrium effects and the freezing of species mass fractions and vibration energy, it is difficult to determine the flight conditions based on the arc-jet tunnel test data by extrapolation. In consideration of this problem and based on the idea of the integrated numerical simulation of the nozzle/test section/test model flow field, the numerical simulation of FD-15 arc-jet tunnel test under the typical operating condition is conducted by solving three dimensional Navier-Stokes equations of the thermochemical non-equilibrium flow. Based on the simulation result, the comparison between the numerical simulation and the tunnel test result is presented, and the problem of extrapolating the tunnel test data to flight as well as the influence of the reservoir pressure on extrapolation are discussed. The result shows:(1) the inflow in the test section has a high level of dissociation, and thus the thermochemical non-equilibrium effect is severe. (2) The tunnel test heat flux result is in between the full catalytic heat flux and non-catalytic heat flux of the integrated numerical simulation, which is reasonable and indicates the validity of the computation method and program. (3)The surface pressure and the heat transfer can be influenced by the installation position of the test model. The surface pressure and the heat transfer flux decrease when the distance from the test model to the nozzle exit increases. (4)When the reservoir pressure is low, extrapolation of the tunnel test heat flux data to the flight conditions by binary scaling (keeping total enthalpy and ρ_∞L the same) is invalid, and the tunnel test heat flux data also shows discrepancies in extrapolation to flight conditions by partial simulation (keeping total enthalpy and stagnation pressure the same), especially under non-catalytic condition. (5)When the reservoir pressure increases, discrepancies in extrapolation of the tunnel test data are significantly reduced with both binary scaling and partial simulation methods.