The invention discloses an automatic construction and dynamic updating method for a geological three-dimensional model, and relates to the technical field of geological modeling. The method comprises the following specific steps: acquiring multi-source geological exploration data; the authenticity of the multi-source geological detection data is judged, and data meeting conditions are extracted for data fusion to establish a geological information database; performing interpolation processing on the three-dimensional coordinate data according to the three-dimensional coordinate data of all the measuring points in the geological information database to obtain three-dimensional data after interpolation processing; calling three-dimensional modeling software to establish a geological three-dimensional model according to the three-dimensional data; after the geological three-dimensional model is established, when data updating occurs in a target area, new stratum information is obtained, the orientation corresponding to the new stratum information is used as a new constraint point, and the geological three-dimensional model is updated according to the structure of the new constraint point and rock attribute information. According to the method, the three-dimensional geological model is constructed based on the multi-source data, so that the visualization accuracy of geological conditions can be effectively improved, and the spatial characteristics of the geological body can be reflected more truly.