Abstract:  Numerical simulation has been an essential tool in the fields of engineering geology and geotechnics.However,it has a weakness,that is,its results of quantitative analysis are sometimes non-realistic,even if they are often acceptable.One of the reasons resulting in the weakness is that the geological model is not perfectly accordant with the realities of complicated geological and artificial objects.To improve the accordance,a new method of building a 3D engineering geological model is proposed.The method is based on boundary representation and suitable for numerical simulation.Firstly,a unitary wire frame,composed of simple arcs,is built.Secondly,the initial interfaces constrained by the wire frame are modified and reconstructed to ensure seamless connection.Then,using the block tracing method,a sealed model,consisting of blocks surrounded by modified interfaces,is generated.In this model,the problems of ultra-thin and sharp-angled blocks are solved to improve mesh quality.Finally,using advancing front technique,each block of the sealed model is discretized into tetrahedrons;meanwhile,combined with rock mass quality spatial classification,the computing model suitable for numerical simulation is generated.As an example,a 3D engineering geological model for FLAC3D is built to analyze the stability of the dam and the bedrock of a hydropower plant.