The buried parallelogramic grating is to embed tilt dielectric film in the waveguide with sub-wavelength cycles. Based on rigorous coupled-wave analysis, the grating is modeled and numerically analyzed. The diffraction efficiency under different polarization states and incident angels is calculated. The result shows that with the TE-mode incidence, the 1st order diffraction efficiency varies between ［0, 37%］ with the film thickness and stays almost the same with the change of incident angles. The other non-zero orders′ efficiencies are below 2%. This feature could satisfy the increasing efficiency required in the head-up display. It could also reduce the energy loss and unwanted image rays. When the incident angle changes between ［45 °, 70 °］ in vertical and ［－15 °, 15 °］ in horizontal, the 1st order diffraction efficiency stays almost the same to maintain the uniform display in different view fields. The effect on the diffraction efficiency is also discussed with the change of polarization, inclination, cycle and materials. This article can provide theoretical guidance in the manufacture of the grating.