A high voltage sensor based on optical fiber Fabry-Perot interferometer and insulating oil is proposed. When high voltage is applied on insulating oil in the container, liquid flow caused by high voltage changes the cavity of the Fabry-Perot interferometer in the oil. High voltage information can be demodulated by using the change of the reflected light intensity. In our experiments, pulse voltage, with the peak of dozens kilovolt in amplitude, the full width at half maximum time of 1 ms and power frequency voltage of 7 kV, are measured. Experimental results show that the output light intensity of the sensor can respond sensitively to such kind of liquid turbulence. The light waveform is nearly pulsed under a pulse voltage. Moreover, the frequency of the output waveform is 50 Hz when the power frequency voltage of 7 kV is applied to the sensor. The sensing method based on optical fiber sensor and liquid flow has a potential application in the measurement of millisecond even microsecond pulse voltage and power frequency high voltage.