Electrostatic voltmeter plays an important role in the measurement of atternating current (AC) and direct current (DC) high voltage. In order to achieve highly precise measurements in a wide range, an electrostatic voltage sensor using Fabry-Perot (FP) cavity interferometry principle is proposed and fabricated. The measurement electrodes consist of a sensor electrode and a high voltage electrode. FP cavity of the sensor is formed by optical collimator and polyester film aluminized outside. When the high voltage electrode is applied, uniform electric field is produced between polyester film and high voltage electrode. Under the pull of electric field, the shape of polyester film is deformed and the length of FP cavity changes, causing the output spectrum shift of the FP sensor. Phase demodulation method is used to obtain high voltage applied to electrode and realize the electrostatic voltage measurement. The experimental results show that the sensor can measure DC voltage and AC root-mean-square voltage in 5~16 kV. The measurement accuracy is 1.21% of 5 kV to 10 kV and 0.61% of 10 kV to 16 kV. The sensor satisfies the requirement of high voltage measurement.