By simulating the Q-switch process of the optical activity crystals in the laser cavity, the experiment setup for studying the electro-optic effect of the optical activity crystals is designed. The phenomenon of interference of the optical activity crystals in the perpendicular polarized light and the parallel polarized light is studied. The optimum configuration for the optical activity crystals to be used as the electro-optic Q-switch in the laser cavity is obtained, and the electro-optic Q-switch is made by using the typically optical activity crystal La2Ga5SiO14 successfully.