With the continuous development of smart cities, 3D vegetation models are increasingly used in urban planning, city design, ecosystem service assessment, and other aspects. City geography markup language (CityGML) is a common semantic information model presenting 3D urban objects, and it can be shared by multiple programs. CityGML is a widely-used open international standard for simulated cities and landscape architecture modeling. Based on the existing CityGML standard for urban levels of details (LODs), this study proposes semantic information model for urban vegetation types (trees, shrubs, ground cover) by analyzing the application requirements at different LODs. The vegetation model consists of above-ground and below-ground parts with plant components (flowers and fruits) introduced into the LOD4. A CityGML-based multi-scale 3D semantic model construction method is proposed, and it can be used for visualization and informatization of plant parts in digital cities to solve the problems with existing vegetation 3D models, such as single function and the lack of unified data collection standard.