In a power distribution network, the traditional single-phase-to-ground fault phase detection method needs to consider the phase sequence and amplitude of voltage to determine the fault phase. However, it is difficult to measure the phase angle in a high impedance grounded fault. As a result, it is more difficult to determine the fault phase. The relationship between the phase voltage and the neutral displacement voltage are analyzed when a single-phase grounded fault occurs in a small current grounded system. This paper proposes a simplified method to detect the fault phase directly and quickly according to the neutral displacement voltage and phase voltages. Finally, a simulation model is built in PSCAD/EMTDC, and the results show that the proposed method can accurately identify the fault phase in the case of different fault resistances.