To solve the problem of electromagnetic interference using piezoelectric in traditional acoustic meas- urement

an optical fiber Fabry-Perot sensor is designed to detect the ultrasonic signal generated by partial discharge （ PD）

and a method of acoustic energy root value is presented to describe the correlation of PD level and acoustic signal. Based on the elastic mechanics theory

vibration characteristics of the circular diaphragm is ana- lysed

and an extrinsic fiber Fabry-Peort （FP） ultrasonic sensor is designed and manufactured. PD signals are gen- erated from plate-plate electrode system

and the PD detection system with FP sensor

PZT and impulse current method is built. Experimental results show that the fiber sensor has the same sensitivity with PZT transducer. The correlation of amplitudes and energy of square root of acoustic signals is analysed

and the results show that correla- tion coefficient of energy of square root of acoustic signals with PD level is more 0. 1 than amplitude with PD level.