We propose a method of enhancing the reusability of the component IPs by separating communication and computation for a system function. In this approach, we assume that the component designers describe mainly the computation part of the component, and the system designer can construct the communication part by using our refinement-based design environment. Moreover, we introduced a concept of the communication architecture template tree (CATree), which helps IP designers to effectively separate computation and communication for a system function. We confirmed that this approach is effective by applying it to a H.264 decoder design.