This paper discusses a theory and its implementation of integrated design object modeling for intelligent CAD. Models from different aspects must be correlated at the level of their background theories, so that the system can derive relationships among models from knowledge about the physical world. The metamodel concept proposed in this paper is a framework for integrating design object models in this manner. In order to implement the metamodel, we need representations of concepts about physical phenomena and a method for reasoning out the relationships among the concepts. Qualitative physics plays two roles for this purpose. The first role is to serve as a representation framework of concepts and their relationships. The second role is to serve as a reasoning method for generating aspect models and deriving qualitative behaviors from the aspect models. The idea of the metamodel is demonstrated by a design system, which provides the designer with physical features to build a primary model, helps to generate aspect models from the primary model, and maintains consistency among the aspect models.