The partial discharge is an effective method to detect the insulation performance of high voltage components, and the degree of insulation degradation can be effectively predicted by the detection of sound, light, electricity and other signals. The optical fiber sensor test system based on the ultrasonic signal detection method of partial discharge is set up in this paper. The Machzehnder interferometer is used to detect the optical path difference caused by the acoustic signals and to detect the micro mechanical deformation in the measurement circuit. The practical test results show that the proposed system has a very high sensitivity, the mechanical deformation at nanoscale can be accurately measured and accurately reflect the ultrasonic signals caused by partial discharge. Using this optical fiber sensing system, the partial discharge of multilayer ceramic devices can be tracked and measured.