Abstract: In order to solve the problems of low sensitivity and poor consistency of extrinsic fiber Fabry-Perot interferometor(EFPI) sensor applied to the detection of liquid dielectric partial discharge ultrasonic signal, according to the multi-beam interference theory and the fluid-structure coupling vibration system, the EFPI sensor is optimized and designed, and the micro-electro-mechanical system(MEMS) processing technology and silicon-glass bonding technology are utilized to achieve a high degree of consistency between the sensor design structure and the preparation structure. The fabry-perper cavity length of EFPI sensor is 100 μm, the diaphragm thickness is 5 μm, the effective confinement radius is 0.23 mm, the first-order natural resonance frequency in the insulating oil medium is 117 kHz, and the static pressure sensitivity is 0.0204 nm/Pa. The experimental results show that the maximum deviation rate of the four EFPI sensors prepared by the method-per-cavity cavity length is 0.043%, the maximum difference rate of the interference spectral modulation system is 0.89%, the first-order natural resonant frequency is exactly the same and consistent with the design calculation results, and the partial discharge ultrasonic signal detection characteristics have high level of consistency. Meanwhile, the efficient detection angle range is −60°~60°, the detection sensitivity of EFPI sensor is 3.75 times that of the traditional piezoelectric sensor(PZT), and the minimum amount of partial discharge that can be detected by EFPI sensor is lower than that of PZT.