The method of traditional grounding phase detection is conducted under the premise of ignoring the asymmetry of the grid. When a single-phase to ground fault via high resistance occurs in the distribution network, the traditional criterion is futile. In response to this limitation, this paper presents a new method of traditional grounding phase detection based on the method of injecting current. When a single-phase to ground fault occurs, a special current injected into the grid, to eliminate the asymmetry of the distribution network. Then the neutral point voltage is only caused by the grounding phase. By analyzing the phase angle of neutral point voltage after injecting this special current, the paper draw the neutral point voltage phase angle varies with the transition resistance. It can be seen that different phase takes place a single-phase to ground fault the neutral point voltage phase angle varies with the transition resistance is not the same That is to say the range of the phase angle of neutral point voltage after injecting the current can be used to detect the grounding phase, especially the high resistance grounding fault detection. Its feasibility has been verified by simulation.