Abstract: A new algorithm of online fault locating suitable for high voltage and long distance same-tower parallel transmission lines is proposed.Based on impedance model of single terminal parallel lines,the influence of distribute capacitance for high voltage and long distance parallel transmission lines is eliminated in the novel method.The solution of differential equation is obtained with integral way and the influence of distribute capacitance on uncertainty of fault locating is solved using iterative method.Simulation results which are obtained by using DPR-2E fault recorder and real time digital system（RTDS） simulator show that it is correct.The algorithm can be used online because it can calculate fast and only need short data window.