Consideration matters on product design and development are remarkably increasing recent years in manufacturing and improvement of the intelligent productivity of design business has become a pressing need for enterprises. Especially, in the design field of welding vessels, which are comparatively large size products, it is not only to concern with the geometric information like drawing, more important thing to be considered for a designer is to treat with the existing design knowledge. But traditional CAD systems can not treat it efficiently because of the shapes-oriented approaches. Thus, there has been a considerable growth of interest in knowledge-based design support systems. Based on object-oriented methodologies and attribute-oriented modeling paradigms, we have proposed the assembly structure as a design object model. This paper focus the discussion on modeling and representation of weld joint, and processing the public design knowledge used in manufacturing deign based on the proposed assembly structure model.