Abstract:A 3D engineering geology modelling and analysis system is designed based on the complex data structure of boundary representation(Brep) and TIN,as well as the GIS technique. The TIN model is used to fit the stratum interfaces. A few methods to build TIN model are supposed,such as the discrete points converting from the contour line and the DEM model. The techniques of intersection,cutting and mending between the TIN model are also discussed. The geological information can be realistically represented by color and texture mapping. Furthermore,the analysis method based on the 3D geological model is presented,including generation of geological section,calculating area and volume of the stratum body. Finally,the 3D engineering geology modelling and analysis system is applied to simulate some projects,such as the coast,slope,hydraulic and hydroelectric project,and excavated highway slope. The results show that the theories and system have favourable reliability and practicability.