Accurate and reasonable assessment of in-situ stress is of paramount importance for the safety evaluation and disaster prevention and control of underground engineering. This paper proposes an in-situ stress measurement strategy that combines ground surface and adit testing and employs mutual verification between different measurement methods, and presents a research scheme that integrates three-dimensional initial stress field inversion to reveal the distribution characteristics of in-situ stress at pumped storage power station (PSPS) site. Taking the Xinjiang Emin PSPS as a case study, the measurement results show that the in-plane maximum principal stress within the tested burial depth ranges from 4.6 MPa to 14.9 MPa, with the orientation being NNE. The spatial stress results obtained by the hydraulic fracturing method and the borehole diametral deformation method are broadly consistent, although some differences remain. The first principal stress at the underground powerhouse site is 12.3 MPa–13.5 MPa, belonging to moderate stress level. The three-dimensional initial stress field inversion, with error within the engineering acceptable range, captures the disturbance effect of faults on the stress field and the stress concentration effect in the river valley, and reveals a “three-stage” distribution pattern of the lateral pressure coefficient of the maximum horizontal principal stress in the rock mass along the water conveyance route. The research findings and approach can provide a scientific basis for the design and construction of key underground structures, and serve as a useful reference for specialized in-situ stress investigations in similar projects.