Abstract: Mach-Zehnder optical waveguide is an important component in electro-optic polymer modulators.Approach of EIM and 2D-BPM are combined in this paper,and using effective index method（EIM） to calculate the transverse refractive index distribution and the effective index of polymeric ridge waveguide.Then proceeding from the Maxwell equation,the basic computing scheme of the finite difference beam propagation method（FD-BPM） is obtained by utilizing the transparent boundary condition and the Crank-Nicholson difference scheme.The TM mode light wave propagation and loss characteristics of the M-Z waveguide are theoretically analyzed,particularly the M-Z waveguide using IPC-E（20wt%）/PSU as it’s core layer.The structure of waveguide is optimized,and satisfactory results are obtained with the method proposed.