When a hypersonic vehicle flies, it will have friction with the atmosphere, ionizing the surrounding air, and producing a plasma sheath containing a large number of free electrons. The plasma sheath will cause the electromagnetic wave to seriously attenuate, which will result in communication interruption and other problems. With the gradual realization of terahertz wave technology, its high penetrability and anti-interference performance provides an important way to solve the blackout problem. Thus, the using of the terahertz wave to solve the blackout problem encountered during vehicle reentry is of great significance to studying the transmission performance of terahertz wave in the plasma sheath. This article refers to the public data of the plasma sheath during the reentry of the RAM vehicle. Considering the asymmetry of the sheath density distribution, a double Gaussian distribution is used to simulate the longitudinal electron density distribution. Based on the SMM algorithm, the article uses the magnetization direction, electron density, external magnetic field strength, collision frequency of the non-uniformly magnetized plasma as variables, and their effects on left-hand and right-hand polarized terahertz wave under normal incidence are studied. The results show that these parameters have obvious effects on the transmission performance of terahertz wave in high-density plasma sheath. The right-hand polarized terahertz wave will produce a power absorption peak near the cyclotron frequency due to cyclotron resonance. Changing the magnetization angle in a certain direction will bring an opposite effect on the transmission rate to left-hand polarized and right-hand polarized terahertz wave. Reducing the magnetization intensity can avoid the absorption peak of the right-hand polarized wave by the plasma to a certain extent. Increasing the magnetization can increase the transmission power of the left-hand polarized wave to a certain extent. Moreover, reducing the collision frequency can narrow the absorption band of the right-hand polarized wave in the plasma and increase the transmission power of left-hand polarized wave. In general, the transmission performance of left-hand polarized terahertz wave in non-uniformly magnetized plasma is better than that of right-hand polarized terahertz wave. These results provide a theoretical basis for investigating the blackout phenomenon. The adjusting of these parameters studied in the article is expected to be able to alleviate the blackout problem to a certain extent.