Theoretical analysis of crystal clad fiber-optic polarizer is presented in this paper. At first, the anisotropic refractve indices of potassium pentaborate at long wavelength region were determined. Then extinction ratio variations with the parameters of single mode fiber and crystal were calculated for the polarizer with only one side crystal clad by using planar dielectric waveguide model, and the whole crystal clad polarizer by using W fiber model, The comparison and the discussion of these two types of crystal clad fiber-optic polarizer have been made.