The utilization efficiency of light energy is affected by the multi-order images during the reconstruction of holograms based on liquid crystal spatial light modulator （LC-SLM）, which leads to the low intensity of single image. A novel method is proposed to improve the diffraction efficiency of single reconstructed image by synthesizing phase hologram and digital blazed grating. The property and principle of wave-front modulation are analyzed by use of digital blazed grating as diffractive optical element （DOE）. The effect of digital blazed grating on the reconstructed image of phase hologram by use of LC-SLM is also described. Holographic optoelectronic display system based on LC-SLM is set up for phase hologram reconstruction. Theoretical analysis shows that, the intensity of single reconstructed image is increased by 1302 per cent by adding digital blazed grating with period of 2 pixels in vertical or horizontal direction, and 4297 per cent with the same period of digital blazed grating in vertical & horizontal directions. The experimental result also verifies that, by the proposed method, the energy intensity of single reconstructed image is increased and the utilization efficiency of light energy is improved.