Research methods: In this paper, the method of analyzing the interferences on the underground communication system by electrified railway was established by adopting the equation of electromagnetic field to activate coupling of underground transmission line and its solution.
Research results: The following mechanism，limitation value，formula and data are obtained and calculated: the mechanism for the interference on railway communication by electrified railway，the limitation value of interfering railway communication by electrified railway，formulas for calculating interference of magnet coupling and interference of earth current，and the data related to causing isolated distance exceeding limitation value.
Research conclusions: The interference on the cable and fiber cable in the railway communication system by electrified railway can be controlled effectively by adopting the relevant protection measures for the cable and fiber cable，therefore，the purpose of electromagnetic protection can be achieved.
2007, Vol. 24 
