The site geological investigation and research work of the Three Gorges Project (TGP) has lasted for more than 50 years, which catches wide attention at home and abroad due to its depth and extent. The research processes, approaches, contents and basic conclusions for the key engineering geological problems of dam site are briefly introduced, including the deep anti-sliding stability of dam foundation, the high slope stability of permanent ship-lock, the surrounding rock mass stability of the main plant of underground powerhouse and the faulted structures. Finally, an overall summarization and evaluation of the research are presented based on the situations of project construction, monitoring and operation.