Abstract: Due to the random nature of the fault location,the truncated error is inevitable when the number that the real fault distance divided by the distance corresponding to one sampling interval is not an integer.So the mechanism of truncated error was analyzed and the corresponding revision method was proposed.Taking the fault location issue of double-circuit parallel transmission lines as an example,the arriving time of the current traveling wave can be determined by the modal current maximum.The error of fault location can be limited up to within one sampling interval by means of derivative calculation on wavehead in the condition of low sampling rate.In this case,the accuracy of fault location can be improved greatly.This algorithm is still appropriate if the error of fault location can be limited up to within one sampling interval by means of the preset wavehead location algorithm.A variety of simulation test results verified the correctness and feasibility of the proposed method.