In order to achieve high precise measurements of electrostatic voltmeter, an electrostatic voltage sensor of fiber Bragg grating (FBG) based on uniform strain beam is proposed. It can achieve temperature selfcompensation of sensor by twin- FBG structure scheme in a special temperature range; the sensor structure system is optimumly designed and prepared by simulation analysis of uniform strain beam and simulation on electric field of sensor system. Uniform electric field is produced using a pair of plate electrode, conductor hemisphere is forced under the pull of electrostatic force and the shape of uniform strain beam is deformed, causing central wavelength of twin- FBG reflection spectrum shift, and realizing the voltage measurement by wavelength difference of FBG. The experimental results show that the sensor can measure direct current (DC) and alternating current (AC) root- mean- square voltages from 5 kV to 24 kV. Moreover, the measurement accuracy is 2.1% from 5 kV to 12 kV and 0.89% from 12 kV to 24 kV, and the fitting degree of the sensing curves is 0.99985. The sensor satisfies the requirement of high stability and high reliability, high precision and strong anti-interference ability and so on.