To enhance the geometric ability of current modeling system, the non-regular precise geometric model is used as the unified data structure to represent and manipulate the wire-frame models, the surface models and the solid models in the algorithms. The authors present the data structure and Boolean operation in this paper. For Boolean operation, accuracy, efficiency and robustness are the main consideration. As the geometric kernel of a feature based modeling system, the algorithm has been implemented in a feature based modeling system named GS-CAD98 on NT platform.