The structure and the properties of the holographic polymer dispersed liquid crystal (H-PDLC) grating were explored and analyzed both theoretically and experimentally. The results of the experiment are consistent with those of the theory. Coupled-wave theory is used to analyze and explain the properties of the grating. The grating was used to flatten the gain of EDFAs and dynamic gain equalization can be implemented with the electrically controlled gratings. The gain from 1530 nm to 1560 nm can be flattened with the fluctuation of the amplified spontaneous emission decreased from 3.3 dB to less than 0.2 dB_ p-p in the temperature range 0-65℃.