Abstract: Optical fiber electric field sensor has the characteristics of small size, good electrical insulation performance and so on. It has a wide and important application in the field of monitoring the states of electrical devices. Traditional dual beam interference based electric field sensors have the drawbacks of low contrast of interference spectrum and narrow width of free spectral line, which lead to the technical bottlenecks of low sensitivity and poor temperature stability. Therefore, we propose a three-beam interferometry(TBI) based electric field sensor. We introduce the working mechanism of the sensor, discuss the influence rule of the structure parameters on the performance of the sensor, and give the optimal structure design method of the sensor with high temperature stability and sensitivity. Experimental results show that the sensor has sensitivity of 1.32 V/(kV·cm^–1) and temperature stability of 2.6 pm/℃. The response to the pulsated electric field shows that the sensor has a wide range of frequency response. This work is of great significance to improving the technical level of all-fiber electric field sensor and popularizing its practical application in engineering.