The temperature of high-voltage cable will seriously affect the use of cable. It is of great significance to monitor the internal temperature of wire core through skin temperature. By analyzing its working principle and demodulation mechanism, it is proved that there is an obvious linear relationship between the temperature and the central wavelength of the fiber Bragg grating. The standard relationship of three core cable is improved by shape factor, the equation between core temperature and skin temperature is constructed, and its accuracy is proved. The fiber Bragg grating real-time temperature measurement system is built. Through 20 ~ 100 ℃ calibration experiment and error analysis, the effectiveness of the temperature measurement system is proved, and the linear relationship between temperature and central wavelength is verified. Through experimental verification, it is proved that the temperature measurement system can effectively realize the temperature measurement of high-voltage cable and distinguish the abnormal cable.