The volume holographic grating is often used as an input/output coupler in a head-mounted display, and its diffraction efficiency greatly affects the imaging quality of the system. Therefore, a new coupled grating structure is proposed to improve the diffraction efficiency of volume holographic gratings, which is composed of an optimized volume holographic grating and a blazed grating. The rigorous coupled wave analysis is used to simulate the new coupled grating structure. The results reveal that compared with the volume holographic grating, this structure increases the diffraction efficiency of transverse electric mode light by 1.5%, the diffraction efficiency of transverse magnetic mode light by 9.4%, and the diffraction efficiency of unpolarized light by 5.3%. In addition, this structure boasts an increase of 0.2° and 0.5° in the full width at half maximum of the incident angle under different polarization states (transverse electric mode light and transverse magnetic mode light), which indicates that the structure has a larger field of view angle.