Aimed at the communication blackout problem that a hypersonic aircraft passes through near space atmosphere, a method that an additional magnetic field is used to change electromagnetic environments of plasma sheath is proposed. According to the data provided by radio attenuation measurement C (RAM C) voyage experiment, a model of plasma sheath is established. This paper analyzes the magnetic field intensity and parameters of plasma including plasma thickness, plasma density, plasma collision frequency to get the reflection and attenuation properties of GPS wave propagation in plasma sheath by numerical calculation. Comprehensive analysis shows that additional the magnetic field around aircraft can effectively solve the "communication blackout" problem especially directed against GPS signal in low frequency. When magnetic field intensity is over 2 T，the transmission attenuation values of GPS signal in plasma sheath are all 5 dB below. The communication state is perfect.