A variety of signal cables are used in railway communication system to connect signal equipments, while HVDC power transmission lines in fault condition and DC side harmonics exert impact on railway communication lines. So the research on the influence degree of railway communication has practical significance to ensure railway transport efficiency. According to the principle of electromagnetic induction of power lines on weak current circuit, the theory and calculation methods of influence of HVDC power transmission lines on railway communication lines are introduced in this paper. Based on the limit of influence of HVDC transmission lines on communication lines in China, the induced voltage and disturbance voltage are calculated and simulated in PSCAD/EMTDC with the changes of different parameters, in which the influence degree of different parameters on induced voltage and disturbance voltage is obtained. Finally, some protective measures are suggested to restrain dangerous effects and interference effects.