The invention discloses a novel power system electric transmission line fault diagnosis method. The method includes the steps that first, fault recording wave signals of an electric transmission line are extracted, and a three-phase current value and a discrete value of an earth current of the electric transmission line are obtained through discrete wavelet transform; then, according to a wavelet function db10, the wavelet coefficient entropy of each phase current is calculated, the sum of the wavelet coefficient absolute entropy of all the phase currents is calculated, and the largest value phase, the smallest value phase and the medium value phase of the three values are determined through comparison. According to the designed algorithm, the type and the phase of a fault which happens to a circuit where input current signals are located are judged. The algorithm relates to three parameters, and the parameters are set through a training set; model accuracy verification is performed through a test set, and meanwhile the parameters are corrected. With the method, whether a fault happens to the circuit and the type of the fault can be fast judged, and therefore good assistance effect is played for on-site dispatch personnel to fast and accurately position a fault area after the fault happens, and the security and the stability of the electric transmission line can be improved easily.