The object-oriented design process has been a hot topic in software development since it will improve product quality and productivity significantly, which is also a major issue in systemon-chip design. In this paper, a design process is proposed for hardware-software heterogeneous systems by reinforcing parallelism, structure, and timing. The management of design ion is also introduced for refinement of hardware. UML is used as a modeling language, and the reinforcement above is gracefully integrated into UML by its extensibility mechanism. An example of architecture exploration and performance analysis is illustrated through the application of the process to an image decoding design. Categories and Subject Descriptors C.4 [PERFORMANCE OF SYSTEMS] General Terms: Performance, Design, Experimentation