Detection distances of the hypersonic aircraft based on a point source infrared detectability were predicted under the ground-based and space-based observation platforms. Two-temperature N-S equations were solved and the fluid-solid conjugation heat transfer technique were used for calculations of the surface temperature. Absorption coefficients of species were evaluated by the line-by-line method, and the radiative transfer equation was solved with the line-of-sight method to obtain intrinsic radiation characteristics of the HTV-2 type vehicle. The detectability of the two platforms was calculated considering the atmospheric transmittance, background and path radiation parameters. Results show that the radiation intensity of the target is determined by surface emissions comparing with the gas radiation. The intensity integrated within the 3-5 μm band is high nearly an order of magnitude than that within the 8-12 μm band. Under the condition of a constant sensitivity, the maximum detection range is strongly dependent on the spectral regions and observation angles. The maximum detection distances under ground-based and space-based stations are 450 km and 1 450 km for the 3-5 μm band, and 300 km and 550 km for the 8-12 μm band, respectively.