When an aircraft reenters the atmosphere at hypervelocity, a plasma sheath that can block communication with the ground is formed due to the air ionization on the vehicle surface. In this study, a plasma sheath model with the inhomogeneous electron density and electron collision frequency is established to investigate the plasma sheath characteristics on the surface of the reentry vehicle. The terahertz wave propagation in the plasma sheaths with different distribution characteristics is discussed based on the idea of the equivalent wave impedance in inhomogeneous media. The effects of different factors on the propagation characteristics of left-handed and right-handed circularly polarized terahertz wave in the plasma sheath are studied. The results show a periodic phase shift of the terahertz wave in the plasma sheath, which is mainly affected by the incident angle. This periodicity has nothing to do with wave polarization but is related to wave position and frequency. The propagation characteristics of the two polarization modes of terahertz waves greatly differ under the same factors at low frequencies. The propagation characteristics of the two polarization modes gradually approach with the transmission frequency increase.