There are many problems in the exploration of underground rock mass structure in pumped-storage hydroelectricity, such as water-involved, complex and changeable topography and high requirements of depth and resolution. A high-density resistivity detection method with strong adaptability, high stability and abundant information was proposed, which could meet the requirements of the detection depth and resolution of the underground rock mass structure of the dam, this method had a high sensitivity to the low resistivity anomaly, and had a significant advantage in the exploration of underground fracture zones and faults. Based on the analysis of three high-density resistivity profiles in the upper reservoir of Yongmu pumped-storage hydroelectricity, the distribution of the base-overlying boundary, fracture zones and faults in this section has been inferred and verified by field drilling, it is found that the inversion results are in good agreement with the borehole data, which lays a foundation for fault division, subsoil boundary confirmation and comprehensive geological interpretation. The results show the feasibility and effectiveness of high-density resistivity method in identifying the pumped-storagehydroelectricity underground rock mass structure.