To enhance the radiation performance of the Beidou antenna in the near-space hypersonic vehicle, the static strong magnetic field is applied to weaken the electron density in plasma surrounding the antenna. In order to demonstrate the effect of this program, a time-domain multi-physical method is proposed. The proposed method firstly analyzes the reduction of electron concentration in plasma sheath by static strong magnetic field with the spectral element time domain (SETD) method, which has spectral accuracy. Then, the electron density after mitigation is extracted to replace the original electron concentration around the antenna. Hence, the distribution of the manipulated plasma sheath can be obtained. Finally, the radiation characteristics of BeiDou antenna installed in the vehicle are analyzed with the conformal finite difference time domain (CFDTD) method. The simulation results exhibit the comparisons of radiation patterns under different conditions. With the plasma sheath, the radiated electromagnetic waves are greatly attenuated, which will significantly affect the transmission of communication signals. Importantly, the radiation patterns are effectively improved with the external static magnetic field, confirming that it provides an effective tool to mitigate the influence of plasma sheath on the radiation performance of antenna in hypersonic vehicle.