The invention discloses an assessment method for influence of an underground power cable on a subway signal cable. The assessment method comprises the steps of: acquiring construction parameters of the underground power cable and the subway signal cable, changing the construction parameters constantly, calculating values of influence on the subway signal cable when a single phase short-circuit fault occurs in the underground power cable under different parameter conditions, acquiring a curve of values of influence on the subway signal cable when the single phase short-circuit fault occurs in the underground power cable, assessing the influence of the underground power cable on the subway signal cable according to the curve of values of influence, and taking corresponding protective measures when the values of influence exceed a specified value. The assessment method can perform quantitative calculation on influence of the underground power cable on the typical subway signal cable, assesses influence of the underground power cable on subway communication, reasonably adjusts construction design schemes of the underground power cable and the subway tunnel signal cable, and improves operation reliability of the underground power cable tunnels and subway lines.