A new type of voltage sensor employing a symmetrical metal-cladding optical waveguide structure is proposed which utilized the sensitive property of ultrahigh-order modes of the metal-cladding optical waveguide. The voltage change can be determined by measuring the reflected light intensity when a direct voltage is applied to two electrodes to modulate the reflected light intensity through the refractive index change of LiNbO3 . The measurement range of voltage is from -800 V to 800 V with linearity of 0.995. The sensitivity coefficient of reflectivity light intensity is about 0.2% V-1. The results show that the voltage sensor has good linearity and high voltage sensitivity. And it has advantages of easy operating and cheap building up in measurement.