In order to solve the technical problem of the traditional electric field sensor limited by its measurement range, a parity-time (PT) symmetric microcavity structure doped by electro-optical medium is designed, and a new electric field sensing mechanism is proposed. The transfer matrix method is used to calculate the transmission spectrum of the structure. A unique amplified defect mode is found. The peak value and wavelength position of the defect mode vary with the external electric field. The same electric field can be measured by using two mechanisms. One is to detect the change of the defect mode peak value, and the other is to measure the change of the defect mode wavelength position. The measurement range is limited only by the breakdown field value of the electro-optical medium, which can range from 0 to 0.06 V/nm, covering almost any possible electric field environment. For the peak-value sensing mechanism, the sensitivity range is 38.042—47.558 (nm/V); for the wavelength position sensing mechanism, the sensitivity range is 18.357—18.642 (nm²/V), and the average resolution in the measurement range is 0.00925 V/nm.