Rock mechanics plays a critical role in the design and construction of hydroelectric projects including large caverns under high in situ stress, deep tunnels with overburden more than 2500 m, and excavated rock slopes of 700 m in height. For this, this paper conducts a review on the rock mechanics contributions to recent hydroelectric developments in China. It includes the development of new testing facilities, mechanical models, recognition methods for mechanical parameters of rock masses, design flowchart and modeling approaches, cracking-restraint method, governing flowchart of rock engineering risk factors enabling the development of risk-reduced design and risk-reduced construction, and initial and dynamic design methods. As an example, the optimal design of underground powerhouses at the Baihetan hydroelectric plant, China, is given. This includes determination of in situ stresses, prediction of deformation and failure depth of surrounding rock masses, development of the optimal excavation scheme and support design. In situ monitoring results of the displacements and excavation damaged zones (EDZs) have verified the rationality of the design methodology.