In this paper, a UML approach applied in the CBC (constraint-based codesign) of embedded systems, which is presented by Chonlameth Arpnikanondt, is analyzed. Some deficiencies of the method when it is applied in the complicated embedded systems codesign are proposed. According to these deficiencies, the meaning of constraint is extended, and a solution is proposed to improve the efficiency in hardware/software codesign and is explained in detail with the example of mart phone system, which is developed by the Institute of Software, the Chinese Academy of Sciences.