When the single-phase high-impedance grounding fault occurs in the distribution line, the traditional phase selection method based on solving electrical parameters is difficult due to the weak fault characteristics. Based on the difference of amplitude and phase angle between the healthy phase and the fault phase in the three-phase current of the additional state of the fault branch, a new method is proposed to reconstruct the three-phase current of the additional state of the fault branch by means of phase space reconstruction in this dissertation. The accurate selection of fault phase can be realized by reconstructing the difference quantization index of phase trajectory diagram in this method, without accurate calculation of amplitude phase angle. The phase selection results are not affected by the operation mode of system neutral point, transition resistance, initial fault phase angle and load current. The feasibility of this method is verified by Matlab simulation and experimental results.