Abstract: Injection method is one of the important methods of distribution network grounding fault protection. However, an actual grounding fault often contains transition resistance, especially in a high resistance grounding fault, the traditional injection current distribution model and fault detection method does not usually work well. In order to solve the problem of single-phase high resistance grounding line protection in asymmetric power grid, a distribution model of zero sequence fundamental current in feeders and a new method for fault line selection in asymmetric power grid are proposed. By decomposing the components of zero sequence current, it is found that in the case of non-metallic grounding fault, the injected current is distributed in each line, and the proportion distributed is equal to the ratio of the zero sequence admittance of the line to the total admittance of the system, which is defined as "sharing coefficient". According to different neutral grounding modes, trajectory distributions of sharing coefficient with the transition resistance were described, and a single-phase grounding fault identification and fault line selection method based on amplitude and phase characteristics of "sharing coefficient" was proposed. Theoretically, this method can eliminate the influence of asymmetry of the three-phase distributed parameters of power grid, and has the advantage of strong resistance tolerance to transition resistance. In practical application, only the injected current needs to be adjusted and the change of zero sequence current of the detected line to be measured, an easy and simple operation.