The hypersonic vehicles will produce plasma sheath when flying in the near-space, and the existence of plasma sheath will seriously interfere with the communication between the ground and the vehicles.To solve this problem, based on the calculation of the spherical cone flow field, a plasma sheath model is established according to the temperature and pressure distribution of the flow field and the air dissociation reaction model. And then based on thefinite-difference time-domain(FDTD) method, the transmission characteristics of terahertz waves in the plasmon sheath at different flight speeds and incident angles are studied. It is shown that THz wave can effectively penetrate the plasma sheath at different flight speeds and incident angles. This study is of great significance for the communication between near-space and hypersonic vehicles.