During flight of hypersonic vehicle, a layer of plasma sheath will be formed around the aircraft due to the high temperature. As the results of turbulence, the plasma sheath is time-varying. In addition, the hypersonic vehicle and plasma sheath keeps a high-speed relative motion with the radar on the ground. The plasma sheath will influence the original electromagnetic scattering properties of the aircraft, which will affect the normal observation of the aircraft from the radar. Therefore, it is significant to study the interaction between plasma sheaths and electromagnetic wave. In this paper, Lorentz-FDTD (Finite-Difference Time-Domain) method is used to analyze the electromagnetic properties of time-varying plasma sheaths in a 2-D case, and the result show that the time-varying and moving plasma will modulate the electromagnetic waves.