A fiber-optic Fabry-Perot (F-P) ultrasonic sensor based on grooved silicon diaphragm for partial discharge (PD) detection in power equipment has been designed and prepared. The parameters of the grooved diaphragm are optimized by finite element simulation. The static sensitivity of grooved diaphragm is 4.09 times higher than that of traditional circular diaphragm,while the resonant frequency is basically the same. The coupling efficiency is introduced to modify the traditional two-beam interference model,and the effect of the F-P cavity length on the contrast of the interference spectrum is studied to improve the acoustic pressure sensitivity of the sensor. A grooved silicon diaphragm with a grooved diameter of 829.44 μm and a thickness of 2.09 μm is prepared by the micro-electro-mechanical system (MEMS). The F-P cavity length of fabricated ultrasonic sensor is 163.600 μm. The acoustic pressure sensitivity of the sensor is up to 357.78 mV/Pa at the resonance frequency of 61.5 kHz,and the sensor performance is verified by combining with the gas insulated switchgear (GIS) partial discharge defect model. The experimental results show that the proposed sensor has the advantages of high sensitivity,good real-time performance, and strong capable of detecting ultrasonic signals.