Based on coupled-wave theory,a new approach of deriving diffraction efficiency equation on reflecting volume Bragg gratings was proposed,On the basis of the derived equation,the detailed theoretical modeling for diffraction of plane and Gaussian beams on reflecting volume Bragg gratings were obtained,and the diffraction efficiencies including plane monochromatic,divergent monochromatic,and polychromatic beams were analyzed.Numerical results show that the angular selectivity could be varied from more than 100 mrad to less than 0.01 mrad,and spectral selectivity could also be varied from more than 100 nm to less than 0.1 nm.When angular divergence or spectral width equals the angular or spectral selectivity,the grating can provide maximal diffraction efficiency of more than 88%.When angular divergence or spectral width is far less than the angular or spectral selectivity,the decrease of diffraction efficiency is insignificant,which is less than 1% of plane monochromatic wave.