An optical voltage sensor is constructed by applying the non-balance fiber Michelson interferometer (MI)-piezoelectric ceramics（PZT）system to alternating voltage. Applying a tunable F-P optical filter to demodulate the output optical intensity variation of MI, which due to the transfer of the piezoelectric deformation, the measured alternating voltage can be obtained. The experimental results show that the sensor has good linear response to the alternating voltage. At the same time, the influence of positioning accuracy of tunable fiber F-P filter and extinction ratio of MI on system detection accuracy are investigated.