The semantics of product design enables to visualize the function of the product and promote communications between the products and the designers. However, the existing theories and methods of product design are lack research on the integration of modeling concepts, domain-specific knowledge, and decision-making. For this reason, this paper proposes a C-D-K theory which is supported by a semantic modeling approach. Firstly, KARMA modeling language, which is a semantics modeling approach, is used to support the formalization of concept space (C) and decision space (D), in which space C is expanded based on the RFLP design framework, and space D is based on PEI-X decision workflow to realize decision problem modeling. Then based on the Open service lifecycle collaboration (OSLC) specification, domain-specific knowledge is represented based on the unified expression of resources in the knowledge space (K), which is used to integrate knowledge to semantics models constructed by KARMA language. Finally, the feasibility and effectiveness of the proposed semantic modeling approach are verified by the case of an unmanned detection vehicle design. From the result, we find the semantics modeling approach enables to integrate semantic models and knowledge based on the C-D-K theory.