Abstract: Based on the Fabry-Perot optical interference principle,the optical fiber EFPI sensor is used to detect PD ultrasonic signals. It has the advantages of high sensitivity and antielectromagnetic interference,and is widely used in the detection of PD in electrical equipment. This paper presents a method to detect local ultrasonic signals in the GIS by using a built-in fiber-optic EFPI sensor. The propagation characteristics of ultrasonic signals in SF6 in the GIS are simulated and experimentally studied by using the finite element method. It is found that when the ultrasonic signal passes through the first diaphragm basin insulator,the attenuation degree reaches about 90%. When the supported basin insulator is used in the GIS,the attenuation of the PD ultrasonic signal is close to that in the pure SF6 gas in propagation. Through the research on the distance detection characteristics of the optical fiber EFPI sensor,it is found that the amplitude attenuation of PD signal measured by different distance sensors are from fast to slow,which is close to the signal attenuation law in simulation. Comparing the detection effect of the EFPI and PZT sensors,we find that the sensitivity of the EFPI sensor is significantly higher than that of the PZT sensor.