Abstract: Aiming at the propagation characteristics of electromagnetic waves in loss media, a modified alternative direction implicit finite difference time domain (ADI-FDTD) method is proposed to solve the problem. The modified method can improve the disadvantage of the traditional ADI-FDTD method, which improves the computational effeciency on the cost of accuracy. The unconditional stability of the algorithm is proved, while the numerical dispersion is also analyzed. The algorithm is validated effectively, and it could also improve computational accuracy, which has been proved by examples comparison. The algorithm is applied to analyze the scattering of a metal sphere in air, on the bottom of ground and sea. The simulation shows that the amplitude and oscillation of the scattering increase in the loss media.