Abstract:Basic geographic database of digital city is changing from traditional two-dimensional form to three-dimensional form. Establishment of 3D model is an important basic work in urban construction. As the core part of 3D model, the quantity of building model is huge, and the production cost is high. Digital photogrammetry technology provides an effective way for collecting building vector datas. In order to reduce the workload of 3D modeling furtherly, structural identification, vector lines of building structures and decent buildings with complex configuration method and algorithm based on the auxiliary building and the development of 3D modeling software system manual should be studied. In this paper, based on the building line of digital city survey, the key algorithms involved in 3D modeling have been studied.