A method for detecting the phase line voltage of a transmission line based on Gauss-Legendre integral provided by the invention includes the following steps: determining the voltage integration path of the phase line of a transmission line, arranging an electric field sensor on the integration path, and detecting the electric field value of the phase line; and building a Gauss-Legendre calculationmodel of the phase line voltage, taking the arrangement point of the electric field sensor as an integration point, and substituting the electric field value of the output end of the electric field sensor into the Gauss-Legendre calculation model to calculate the phase line voltage of the transmission line, wherein a phase line voltage calculation model is shown in the description, Phi(B) is thephase line voltage of a target transmission line, b is the distance from the phase line of the target transmission line relative to the zero potential, and E(b / 2+b / 2*tk) is the electric field value ofthe integration point. The accuracy of phase line voltage calculation can be improved, which is conducive to the accurate scheduling of a power system and the accurate evaluation of the transmissionperformance of a transmission line. Moreover, the algorithm is simple, the result is reliable, and the security risks in the traditional mode can be avoided.