Based on the mode coupling theory of the titled fiber Bragg grating with the numerical analysis methods, the tilted angle and modulation index on the effection of tilted fiber grating reflectivity spectra of front-back core mode coupling and characteristics of tilted fiber grating reflectivity and transmission spectra for core mode and radiation mode coupling on the condition of different tilted angle, index modulation and grating lengths for different polarization are discussed. The results of the study show that different incident lights with different polarizations are exactly the same for front and back core mode couplings. Incident light of s polarization and p polarization state should be taken into account for the radiation mode coupling, because reflectivity spectra envelope are affected by modulation of extinction coefficient and incident light with different polarizations have different extinction coefficients. Moreover, the greater tilted angle is,the more differences for the extinction coefficient of the incident light with difference ploarization is.