In order to avoid complicated transformations and convolutions compared with Z-transform ADI-FDTD and the PLJERC-ADI-FDTD method, the high order ADE-ADI FDTD method for unmagnetized plasma is proposed. The fourth-order spatial central difference approximation technique is used in the proposed method to reduce the numerical dispersion of the ADI scheme. The iteration method for solving equation set improves the computational efficiency. The proposed method can be easily extended to analyze other media through changing the coefficients of the auxiliary difference equation of polarization current. The validity of the proposed method is tested by calculating the reflection and transmission coefficients of a plasma slab. The simulation results show that the computational accuracy and efficiency of the proposed method are higher than those of the PLJERC-ADI-FDTD method. The plasma sheath around a hypersonic blunted cone is established by CFD-FANSTRAN, and the reflection, transmission, and attenuation coefficients of the modeled plasma sheath against frequency under different Mach numbers and heights are calculated through the proposed method. The backward RCS of the plasma sheath is also calculated through the proposed method. The electromagnetic wave propagation and scattering characteristics of the plasma sheath are analyzed via the calculation.