There are problems of high incidence of high-resistance grounding fault in resonant grounding system and major difficulty in zero-sequence voltage detection. Thus a direction detection method for a high-resistance fault of a resonant grounding system based on the voltage polarization of the fault phase is proposed. Using the high-impedance fault equivalent circuit of the resonant grounding system, the polar relationship of zero-sequence current on both sides of the fault point and the fault phase voltage during the transient process is analyzed. It is found that the voltage of the fault phase has a high degree of similarity with the zero-sequence current upstream of the fault point, while it has a low degree of similarity with the zero-sequence current downstream of that point. Given this, the fault phase voltage can be used as the amount of polarization. The direction of the fault can be detected by analyzing the similarity between the current measured at the detection point on the fault line and the voltage of fault phase during the transient process. Compared with previous fault detection methods, this method improves the reliability of the high-resistance grounding fault detection in the resonant grounding system. Digital simulation and field manual tests verify the feasibility of the method. This work is supported by National Natural Science Foundation of China (No. 51477184).