Based on the leaky mode resonance theory,the physical mechanism of producing the broad angular spectrum of Multilayer Dielectric Grating (MDG) in the -1 st order reflection diffraction direction is presented in this paper.It is found that the thin match layer would improve the bandwidth of angular spectrum effectively.A good result of ±11 degree near Littrow angle 37.9 over 90% diffraction efficiency centered at 1040nm is obtained,and the parameters of the result have excellent fabrication tolerance.The Fourier modal method is employed for calculating the diffraction efficiency.