Based on the mode coupling theory, the effect of titled angle on the characteristics of spectrum of fiber grating is proposed. The numerical modeling method is performed by using the software, OptiGrating.By considering the reflection and the transmission spectra, we find that the central wavelength shifts to the long-wave band, the reflectivity of Bragg wavelength decreases, the cladding mode couplings are enhanced,the transmittance becomes larger,and the group delay decreases intensely with the increase of the titled angles. This conclusion provides a theoretical guidance for the design and optimization of fiber grating.