A straight waveguide optical voltage sensor for measurement of power frequency voltage based on Y-cut LiNbO3 waveguide is proposed. Using the Pockels effect of LiNbO3 crystal and adjusting the optical bias to [π2], linear result can be achieved. Making use of the waveguide′s distinguishing feature that optical fiber can couple with waveguide directly, all optical devices are connected with optical fiber so that the optical path is simplified. Both the sensor′s principles and the output/input characteristics are analyzed. The power frequency voltage in the range of 100~3000 V is measured by using this sensor. The temperature dependence is researched preliminarily, and in the range of -40 ℃~60 ℃, transformer ratio is 5.29%. The measurement results show that this kind of voltage sensor is suitable for measurements of high frequency voltage.