Finite-difference time-domain (FDTD) method is used to simulate the light propagation through liquid crystals. The computation window is truncated by the perfectly matched layer absorbing boundary conditions. The incident fields on left connecting boundary and right connecting boundary between total-field region and scattered-field region are calculated independently to introduce plane wave for non-periodic structures. A split-field 1-D auxiliary FDTD method is proposed to calculate incident fields on those boundaries,where the medium are inhomogeneous and anisotropic. Combined these techniques together,plane waves are applicable for non-periodic liquid crystal devices. The simulation results show that the maximum leakage of transmissivity into scattered-field region is less than 3% for twisted nematic cell in on state at 30° incidence. The approach is proved effective for the analysis of optical properties of non-periodic inhomogeneous anisotropic medium.