Abstract: In view of the communication black barrier problem faced by near-space hypersonic vehicles, the flow field around the return capsule of the Soyuz spaceship is simulated, and a plasma sheath model and an ionization model are established according to the distribution of the field pressure and temperatures. The transmission characteristics of the terahertz waves within the range of 0 to 3.5 THz at different flight speeds and different incident angles are analyzed using the scattering matrix method. It is shown that the terahertz waves can penetrate the plasma sheath well with little dependence of the Mach numbers and the incident angles, and the transmission loss decreases with the increase of the frequency. The result provides some insight in dealing with the blackout problem and realizing the full-time communication among near-space hypersonic vehicles and their real-time detection.