Traditional component design methods pay much attention to component?s usefulness, while usually ignore the optimization on component?s usability, such as reuse cost. The aim of this paper is to present a method of component reuse cost optimization. For that, a feature-based component model is firstly introduced to express the reusable semantics of component, with emphasis on reuse mechanism based on variation point. By analysis of constituents of component reuse cost, the optimization goal, i.e., increasing the proportion of fixed part of a component, is put forward. Then a component optimization method based on component instance set decomposition (CISdecomposition) is presented, i.e., according to the reuse frequency of every component instance, separate those instances with higher reuse frequency out to get semi-instantiation components., hence avoids multiple instantiation and feature item implementation in the every reuse process, thereby reduces the reuse cost.