Holographic polymer-dispersed liquid crystal (HPDLC) is a kind of switchable volume holography. It can be manufactured according to the photo-initiated polymerization-induced phase separation. HPDLC is composed of parallel, periodic polymer-rich and liquid crystal-rich planes. The diffraction efficiency can be modulated by the application of electric field. HPDLC devices are potentially useful for optical communication, information storage and display. How to increase the diffraction efficiency is the key to application. We investigated the dependence of diffraction efficiency on the refractive index of the polymer, exposure intensity, liquid crystal loading and temperature. The best conditions were found to make the diffraction properties optimized. Now the highest diffraction efficiency was 802%. The HPDLC morphologies were also observed and analyzed by scanning electron microscope (SEM).