Abstract: The arch dam is an important dam type among high dams with complex geometry,having different sections in the vertical direction and the horizontal direction. Tasks such as arch dam BIM modeling,pouring bin modeling and construction unit shape extraction involve many shape parameters,complex block conditions,and large amounts of data. Based on the secondary development of CATIA,this paper puts forward the method of parametric modeling of dam body,construction block modeling and shape parameter extraction. Based on an analysis of the parametric logic of the dam construction unit,this paper draws up the dam model sectioning plan and uses the CATIA Automation API interface to implement the arch dam parametric modeling,model sectioning and construction unit construction in the C# programming environment. As a result,attribute parameters such as the surface area,volume and corner space coordinates of the construction unit can be dynamically updated according to the needs of project management during the construction period,which can help predict the construction progress and strength of the dam and guide the construction in a scientific and orderly manner. It also provides an efficient and easy-to-use tool for sectioning complex arch dam model construction units and shape parameter analysis.