The perfectly matched layer (PML) absorbing boundary conditions were extended from 2 D TE/TM modes problem to the case of 3 D hybrid modes transmission problem. Scattering characteristics of 3 D discontinuity structures in microstrip lines were successfully investigated. Numerical results show that the presented 3 D PML absorbing boundary condition maintains the advantage of wide band and high accuracy of ordinary 2 D PML. This technique can be further used in the FDTD analysis for complicated structures.