Abstract: The Navier-Stokes equations are solved in this paper by using the AUSMPW+ scheme and the electron density distribution in the plasma sheath is given at different flight speeds. Based on the modified Wentzel-Kramers-Brillouin method(WKB) method, the amplitude-frequency characteristics of electromagnetic signals are analyzed and the phase-frequency curve and the group delay curve are also presented. Numerical result shows that the faster the vehicle speed is, the higher the electronic density is, and attenuation coefficient increases. The phase frequency characteristics of radio wave in the plasma sheath are affected by the collision frequency and plasma frequency. The group delay reaches the maximum near the plasma frequency.