By tracking and measuring the ground parameters of the system, the correct phase selection is achieved when neutral point ungrounded system single-phase fault occurs. Because of the asymmetry of the system parameters, the neutral point of the system will produce a certain voltage shift during normal operation. When the neutral point power frequency voltage changes, by adding a resistor with appropriate resistance in the neutral point and gathering the amplitude and phase of the neutral point voltage before and after inputing resistance, accurate measurement of the system to ground conductance and to ground capacitance are achieved. According to the twice measurement of grounded parameters and the base frequency voltage of the neutral point, the grounding fault phase is selected out with calculation. Matlab simulation shows that the method can accurately measure the parameters of the system to ground and select the fault phase when the single-phase grounding fault occurs.