A hierarchically structured constraint-based data model for solid modelling in a virtual reality environment is presented. The data model integrates a high-level constraint-based model for precise object definition, a mid-level CSG/Brep hybrid solid model for supporting hierarchical geometry abstractions and object creation, and a low-level polygon model for real-time visualization and interaction in the virtual reality environment. Constraints are embedded in the solid model and organized at different levels to reflect the entire solid modelling process from features and parts, to assemblies. This model not only provides precise object definition, but also supports real-time visualization and interaction in the VR environment. Furthermore, it has the potential to obtain precise 3D interactions and precise constraint-based manipulations can be deduced from the data model to carry out precise solid modelling in the VR environment.