In this paper, the predictive analysis and observational construction for the large-scale underground powerhouse cavern complex in Tianhuangping pumped storage power station are presented. The predictive analysis was carried out in three dimensions by FEM that simulated the actual staged excavation procedures. The analysis provides the sufficient information on the deformation evolution and the potential yielding zones in the cavern rocks. Based on the analysis results and the geological observation as well as the instrument measurement made during the construction, the design supporting parameters for the safety of the cavern rocks were adjusted timely. As a result, the underground powerhouse complex was successfully constructed.