A semivcetorial method based on a variable transformed Galerkin method is proposed for optical waveguides. It is successfully applied to analyze the eigenvalues of rectangular and rib optical waveguides. The modal propagation constants and field distributions of rectangular and rib waveguides are presented. The calculated results agree well with the published data. Adopting a proper variable transformation, the artificial boundary condition is avoided, and the polarization characteristics of the mode field are displayed.