A photonic crystal optical switch based on the electric field control character of the liquid crystal (LC) is proposed and investigated numerically. With the transfer matrix method, it is demonstrated that the band gap appears shifted by varying the angle θ which was between the electric field and the vertical incident light and ranged from 0° to 90°, and the transmission of the 1550nm communication wavelength as the angle θ changes is discussed. It is found that the proposed optical switch is achieved by con controlling on-off of the extra electric field.