Abstract: Zaodu river is a provincial boundary river, and the is located in the transition zone of Sichuan Basin and the Yunnan Guizhou Plateau; with large drainage area, rich inflow and complex geological conditions. In order to better development and utilization of the water resource, Chongqing city started Zaodu prophase research of reservoir planning, including five aspects of hydrological, geological conditions, flooding programs, development programs and functional tasks. Study on the engineering geological conditions of reservoir is one of them. Based on the analysis of reservoir geological and hydrogeological conditions of left interstream block, for different geological rock group, it is divided into different hydrogeological unit to evaluat, refine evaluation methods, enrich the content of the evaluation. The results show, exists groundwater watershed in left interstream block, is far higher than the water level in the reservoir early. It will not leak to Songkan river after impound, which laid the foundation for the smooth development of the next phase of work.