Based on 3D geological modeling technique, rapid modeling technique of hydraulic structures, and computer supported collaborative design technique, the 3D geology-hydrotechnics cooperative design system of hydraulic and hydroelectric engineering is implemented by the object- oriented method. The system includes four modules: 3D geological modeling, hydraulic structure modeling, engineering-geological analysis and design, and database management. The modeling modules offer the analysis-design module different kinds of 3D models. Then, comprehensive analyses and cooperative works among different specialities can be realized, such as 3D slitting analysis, treatment analysis of fundamental surfaces, arrangement analysis of underground structures, slope cutting analysis. It can offer technical supports to 3D design of hydraulic and hydroelectric engineering.