Optical fiber sensors are of splendid strength for electrical field intensity sensor due to characteristics including the immunity to electromagnetic interference, lightweight, high sensitivity, and large bandwidth. In this paper, we proposed an electric field intensity sensor based on Mach-Zehnder interferometer (MZI) based liquid crystal (LC) filled photonic crystal fiber (PCF) embedded in optical fiber ring laser (FRL). The air hole of PCF combines the LC and fiber core together. When LC is introduced into air holes, it can maintain the waveguide based on external parameters. The photonic bandgap effect significantly improved the sensitivity between light and external electrical field intensity. Thanks to the FRL demodulation, a high signal to noise ratio (SNR) spectrum about 35 dB is obtained. Besides, in comparison with traditional LC-PCF structures, the sensitivity of ours is as high as 1.1 nm/Vrms which is about twice than traditional sensors. At the same time, the stability of proposed sensor was verified which fluctuation was 0.15 nm around 2.5 hours. Therefore, our structure is expected to practical applications in remote electric field monitor and such electric modulate electro-optical devices.