A new kind of optical switch is devised. The switch bases on one-dimensional photonic crystal doped by electro-optical material. The transmission properties of the structure are studied by eigen matrix method. For light with a special frequency,the on-off function of light can be achieved by putting electric field on the electro-optical material. For alternating electric field,the structure periodically exports pulses. The interval period of pulses is just half the period of external electric field.