Aiming at the problem of how to acquire components from existing systems, this paper proposes a decomposition method for object-oriented systems based on iterative analysis of the directed weighted graph. This method uses the directed weighted graph as the representation of object-oriented systems, and an iterative algorithm for analyzing the independence of sub-graphs at different granularity levels. Those highly independent ones are chosen as candidate components. Experimental results show that this method is effective and can improve the existing decomposition methods in terms of accuracy.