In order to achieve a temperature sensor with a higher sensitivity, a theoretical model is proposed. The theoretical model is based on parity-time (PT) symmetry structure with a defect cavity composed of thermo-optical material. The refractive index of thermo-optical material is dependent on temperature. The changes of temperature will influence the transmittance of the defect mode in the structure. The transmittance spectra are calculated by the transfer matrix method. It is found that with the change of temperature, the transmittance value of the defect mode changes much larger than the location changes of the defect mode. Thus, the change of transmittance value with temperature is used for temperature sensing. Due to the unique gain amplification of the structure, the maximum sensitivity of the sensor is 6.82 dB·K -1. and the detecting range can reach 44.4 K. Through the modulation of structural parameters, the sensor can work with high sensitivity in small temperature range, or with low sensitivity in big temperature range.