Steam pipeline in thermal power plant is long-distance and high-temperature, so it is difficult to find the leakage point. A distributed temperature sensor system is built to monitor the temperature field of steam pipeline. The system can demodulate the temperature from the reflected light affected by the pipeline temperature according to the Raman principle, and the position of measuring point is confirmed through optical time domain reflection technology. Finally, Kalman algorithm is used to de-noise the temperature signal, the result show that it can reduce the system signal fluctuation to 1℃