The diffraction efficiency of the holographic polymer-dispersed liquid crystal (H-PDLC) grating can be adjusted by the applied electrical field. Doping Ag nanoparticles (NPs) can effectively reduce the driving voltage of the grating. Due to the influence of polymerization kinetics, Ag NPs are distributed unevenly in the grating, namely, the distribution of Ag NPs in the polymer and LC area is not uniform and exhibit different electric field control characteristics. The relationship between the threshold driving voltage and the frequency of the applied field can be studied by equivalent circuit model. According to Wagner-Maxwell effect, in this paper, the equivalent circuit model of Ag NPs surrounded by LC and polymer, respectively, was established. Under the condition of different concentration of Ag NPs within the LC area, the relaxation time and relaxation frequency of Ag NPs doped H-PDLC grating was studied. The low driving voltage can be further obtained by adjusting the frequency of applied electric field. The distribution of Ag NPs in the grating can be determined by the optimum driving electric field frequency range, and it is confirmed that the Ag NPs are concentrated in the LC strip and distributed in a small amount in the polymer stripes.