A Fiber Bragg Grating (FBG) is increased in the optical cables, which can be used for monitoring the cable real-time temperature. Finite-element method is used to establish the temperature field model of optical cables. The tunable laser was used as source, and some fiber Bragg gratings with same center wavelength were used as system temperature sensor. In optical cable lines when the temperature is abnormal, the reflected grating center wavelength will shift. By detecting the center wavelength offset of the reflected light, the size of the grating temperature change can be determined. Grating at different positions reflected optical signals needs different time. By detecting and calculating the interval time of reflected light, the location and the temperature of the grating whose temperature has changed will be obtained. Experimental results show that grating temperature sensitivity reaches 11.4 pm/℃. The deviation between the measured temperature and the actual temperature is within 3% range.号处理等方面的研究。成像系统研究”(F2010001268）；河北省科学技术研究与发展计划项目“传感光电缆的开发与应用”资助(10213509D)