Abstract: In view of the problem of ineffective selection of asymmetric mine neutral point ungrounded system while high resistance grounding occurs, a fault phase selection of mine power supply system based on frequency distribution theory was proposed. Each phase voltage after the fault of the first 1/2 frequency cycle was collected, and extended Prony algorithm was used to fit the collected data, then the frequency distribution theory was used to process the sampled voltage of each phase. On the basis, frequency distributions of voltage of each phase were obtained by Bessel formula, and the fault phase was selected by comparing the magnitude of the frequency distribution. The results of Matlab simulation and adaptability analysis show that the proposed method has high accuracy and is applicable to fault conditions of low impedance grounding and high impedance grounding. It has strong adaptability to noise interference and data window length, and is not affected by sampling frequency and group distance.