To guarantee the design quality and improve the design efficiency of mechanical products, taking arc water chamber of steam turbine condenser as example, the paper researches the key technologies in the development process of parametric design system, which can generate both 3D models and associated 2D drawings automatically. Adopting database as the interface of UG and AutoCAD, 2D/3D bidirectional associated relationship is established across platforms. A nonpermanent record is set within the database to save parameters temporarily. Dynamic storage and invocation of parts information is realized by introducing linked-list data structure. Automatic assembly method based on named datum is proposed. Development process and insertion algorithm of modularized geometric figure are also presented. The experimental result shows that this parameter-driven software is a successful application of computer-aided design.