The concepts of polymer dispersed liquid crystal (PDLC) and stressed liquid crystal (SLC) are introduced; the three kinds of definitions, i.e., “positive piezo-optical effect”, “negative piezo-optical effect” and “inverse mode piezo-optical effect” of PDLC switchable glass are given. The new types of stressed switchable glass samples of negative piezo-optical effect and inverse mode piezo-optical effect are prepared. The experimental results show that the haze is above 90% in a scattering state and the transmittance is nearly 30% in a translucent state. The principle of piezo-optical effect is analyzed with polarization microscopy. The results show that the vertical surface pressure or stretching stress applied to the sample will result in the special reorientation of LC molecules in LC droplets, which causes the optical characteristics of the sample to change significantly. The mode of vertical stretched liquid crystal droplet is proposed, the computation results and graph plotting conform with the results from the micrographs of polarizing microscope very well, so that the experimental phenomena are reasonably explained. The research on SLC piezo-optical effect has the fundamental significance for studying the PDLC and the application value for developing non-electro-optic switchable glass.