Abstract: An improved alternative direction implicitfinite difference time domain (ADIFDTD) method to simulate the electromagnetic characteristics of the nonmagnetized plasma is presented. The scattering characteristics of a perfectly conducting cylinder coated by a layer of unmagnetized plasma are investigated by this method, which provides a certain theoretical guidance to plasma stealth technology. By bringing the central difference operator into the discrete treatment of auxiliary equations and using the complete electromagnetic (EM) fields in the FDTD iteration in the full electromagnetic problem space, this method avoids the timeconsuming calculations and obtains the unconditionally stability. Numerical experiments show that this method not only improves accuracy and efficiency over the conventional explicit FDTD methods, but also spends much less computational time than the ADI-FDTD method proposed in the recent reference based on the same accuracy.