The Brillouin frequency shift is linearly related to the temperature change along the single-mode fiber. Based on the linear temperature sensitivity, the Brillouin optical time-domain reflectometry (BOTDR), as one of the distributed optical fiber Brillouin sensing system, can realize detection of temperature distribution along the existing fiber cable in the railway communication system. Three kinds of cables with different cablecasting styles, including cement cladding, iron piping and directly buried laying, are positioned and tested, and temperature change curves are obtained. Temperature variation for the three kinds of fibers is 10, 8, and 6 ℃, respectively, and the temperature rising rate is 10, 8, and 1 ℃/h, respectively. The experimental results show that the BOTDR sensing system can reflect the trend and the rate of temperature change, and can be used for on-line temperature monitoring on railway communication fiber cables.