In this paper, the plasma electron density and collision frequency are calculated based on the flow field simulation of RAM C-III air vehicle, and an inhomogeneous plasma model is established according to the calculation results. The effects of plasma density, plasma thickness, plasma collision frequency and external magnetic field on the propagation characteristics of terahertz wave in plasma are analyzed using scattering matrix method. The results show that the propagation loss increases with plasma electron density and plasma thickness, while the transmittance decreases first and then increases with the increasing of collision frequency. When an external magnetic field is applied, the propagation characteristics of the left-handed polarized terahertz wave will be improved, while for the right-handed polarized terahertz wave, the application of magnetic field induces an absorption peak, which shifts to high frequency range with the increasing of magnetic induction intensity. This work may make a contribution to solving the problem of communication blackout.