The subject of this thesis is the development of the extended CAD model structure. Extended CAD model consists of the design knowledge and parametric CAD model coupled together. As the basis for the development of the design knowledge structure STEP standard was used. Realization of the design model structure is achieved through usage of the object oriented programming approach. Parametric CAD model is created in feature based parametric CAD modeler. Extended CAD model exhibits kvazi intelligent behavior realized through usage of the rule based inference engine. Parts of the extended CAD model coupled with inference rules make the unique whole and in this way behaves as an object in the design process. The main result of this research is the proposition of the design knowledge model. The proposed model of the design knowledge is divided into logical groups as follows: • elements – features and parts that constitute the product version, • rules – set of definitions that describe the product version, • documents – digital and physical documents that makes or are connected to certain design knowledge, • applications – external programs related to the product version, • settings – definition of allowable limits or range of values for parameters, definition of units and material properties, • constraints – definition of required existing parts in assembly and geometric constraints for part assembling, • relations – definition of the initialization of the model parameters. The elements of the design knowledge model are mapped to the classes of the object oriented model. The proposed model is implemented using the Pro/ENGINEER, JAVA programming language and the J-Link libraries.