The large size liquid crystal droplet of polymer dispersed liquid crystal (PDLC) films with piezo-optical effect is prepared, the photographs of polarization microscope with press compared with that one without press are given. The model of compressed liquid crystal droplet is proposed, the order of flattening that liquid crystal droplet turns from pellet to the flat one after compressed is defined, the relation between the order parameter and order of flattening with compressing is calculated. The transmittance distribution of liquid crystal droplet birefringence is simulated in Fortran, and the graph is made with Origin software, the results of computation and graph plotting conform with photographs of polarization microscope compressed, further more, the principle of piezo-optical effect of polymer dispersed liquid crystal films is presented.