Transformer is widely used in substation high-voltage equipment, including potential transformer (PT) and current transformer (CT). Traditional inductive and capacitive potential transformer are bulky and prone to explosion, which may not only damage nearby equipment, but also pose a threat to the safety of substation personnel. Optical voltage sensor based on inverse piezoelectric effect and fiber Bragg grating sensing can achieve better linear performance, wider dynamic range, lighter weight, smaller volume and higher security. However, the lead (plumbum) zirconate titanate piezoelectric ceramic (PZT) greatly restricts the minimum detection threshold. Therefore, in this paper, a simple two-stage lever amplification mechanism is used to amplify the output displacement of piezoelectric ceramics. The performance of the sensing system is analyzed and verified by finite element simulation and DC and AC voltage tests. The amplification mechanism can improve the response ability of the sensor to the voltage signal, reduce the requirements for the inverse piezoelectric properties of PZT materials and the resolution of the grating demodulator, so that the sensor can break through the existing detection limit and meet the requirements of more precise applications.