In this paper, attention was focused on the 3-D higher- order alternating-direction implicit finite-difference time-domain (ADI-FDTD) method using the higher-order spatial difference. Firstly, the numerical formulation is presented. Secondly, the numerical dispersion relation is obtained analytically. And then the numerical dispersion is investigated as a function of the mesh resolution and the time step. Finally, three kinds of cavity problems are simulated as numerical examples. It is found that the higher-order ADI-FDTD method is more accurate than the conventional ADI-FDTD method. In addition, the proposed method does not encounter stable problem.