Abstract: This paper introduces a novel type of optical fiber EFPI ultrasonic sensor that can be embedded into high-voltage electrical equipment, such as transformers and GIS. This novel type of optical fiber EFPI ultrasonic sensor can detect partial discharge ultrasonic signals under different temperatures and pressures conditions.The novel sensor adopts the all-quartz welding process. A hole is opened in the F-P cavity to allow the insulating medium to enter the F-P cavity, which balances the pressure difference between the two sides of the quartz diaphragm due to the temperature and the density of the insulating medium. In addition, an aluminum film is partially plated on the inner surface of the quartz diaphragm to increase the light reflectivity of the inner surface of the diaphragm and improve the sensitivity of the sensor. The temperature, frequency, sensitivity and other performance of the sensor are verified through using the novel sensor to test at different temperatures and different distances.The novel optical fiber EFPI ultrasonic sensor provides a new detection method for detecting partial discharge inside high-voltage electrical equipment. The good results have also been achieved in practical applications.