This paper proposes a new set of alternative direction implicit finite_di fference time_domain (ADI_FDTD) equations. In conventional ADI_FDTD, the update equation is related to several field components in cells nearby, which will lead to some difficulties in two regions:1) around the boundary region between the p erfectly ma tched layer (PML) and the scattering field; 2) around the adjacent bounda ry. Especially, in the region around the adjacent boundary, owing to the inciden t wave, we shou ld make a judgment about the situation of every component and modify the update equation. It is potential to make a solution to one_dimensional or two_dimension al problem. However, in three_dimensional (3D) analysis, one equation concerns w ith el even components and there exist several tens of cases to be modified. This makes the scheme very tedious and impossible to realize. This paper adopts the spli t field difference formation in the whole computation regime to analyse the sca ttering problem. Because the equations in the scattering field region have the same expr essi ons as those in PML absorber except for some coefficients, the boundary in the r egion mentioned above can be ignored. Due to simplicity of the split field equation, the new ADI_FDTD formula in 3D problem has only five compon ents to be cons idered and four modifications at the adjacent boundary to be made. Finally, we utilize this new method to compute some electromagnetic scattering numerical examples, and the results are in excellent agreement with those ob tained w ith other algorithm and the measured data. Moreover, the new method have 6-7 tim es higher efficiency in terms of the CPU time.
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