A temperature sensing system based on intracavity modulation of fiber laser is reported in this paper.The Sagnac interference structure based on sing le-mode-polarization-maintaining-single-mode (SPS) is inserted into the inn er ca vity of the fiber laser as a filter and sensor,and the high-resolution tempera t ure measurement is realized by using the modulation technology of the inner cavi ty of the laser.The SNR of the sensor system is 59dB,and the FWHM is less tha n 40pm.The sensitivity of the sensor system is measured to be 0.641mW/℃ fro m 40℃ to 80℃,and the temperature resolution achieves 1.56×10－6 ℃.Th e sensor system has the characteristics of simple structure and stable output,whi ch is expected to be used in industrial production,environmental monitoring,ma rine scientific research and other fields.