The polarization effect of Schmidt prism caused the two different polarization states in one beam. The field intensity distribution of diffraction of the ridge with the effect of polarization can be obtained in the way of introducing the integral equation of diffraction of ridge. It is shown that the optical field distribution distorted severely under the effect of polarization and diffraction passing through the Schmidt prism. The influence discipline of the result of diffraction with the variational azimuth of the incidence light is analyzed in detail. In the experiment, the diffraction patterns of two peaks are splited by the diffraction of zero order with the light beam emitting from a He-Ne laser passing through the Schmidt prism. The polarization effect and the diffraction of ridge have destroyed severely the light transmit both in the analysis of experiment and the theory.