A new three-dimensional finite difference beam propagstion method (3D-FDBPM) is proposed.We use the finite difference technique and the Alternating Direction Implicit Method(ADI)to deal with the scalar paraxisl wave equation and establish the 3D-FDBPM. This method is very robust and can be used for various Photonic devices with complex index profile and allows large propagation steps along the propagation direction of the waveguide structure with uniform waveguides. This method is used to analyze the electrooptically induced waveguide configuration and single-mode fiber.