Polymer dispersed liquid crystal (PDLC) is a thin film formed by liquid crystal (LC) droplets embedded in a continuous polymer matrix in the form of micron-sized droplets. The use of click chemistry method to prepare PDLC can avoid the problems of dye decomposition caused by traditional photopolymerization-induced phase separation. In this study, four polyethylene glycol diacrylates (PEGDA) of different alkyl chain lengths were used as raw materials to synthesize PDLC films through thiol-ene click reaction and thiol-isocyanate coupling reaction, to study the effects of different alkyl chain length olefin monomers on the electro-optical properties of PDLC films. The results showed that as the chain length of olefin alkyl chain in the system increased, the threshold voltage (Vth) , saturation voltage (Vsat) and contrast ratio (CR) decreased, while off-state transmittance (Toff) and on-state transmittance (Ton) increased. By selecting olefin with appropriate alkyl chain length, PDLC films with good electro-optical properties can be prepared.