With the increase in the traction power of high-speed railways, the power-frequency electromagnetic interference of traction current to the signal cables becomes increasingly more severe. In this paper, the calculation model of the magnetic interference to signal cable was established on the MATLAB/Simulink platform based on the multiconductor transmission line theory. This model took SPTYWPL03-8B 8-core twist signal cable as an example and the power-frequency interference of external current to the signal cable was analyzed theoretically. In addition, experiments on electromagnetic interference of double-ended and single-ended signal cables were performed to validate the simulation model. Experiments showed that the relative error was less than 5\% by comparing the experimental and simulation results. This research is helpful for the quantitative analysis of the power-frequency electromagnetic interference of traction current to signal cables.