Abstract: Abstract: With the help of the concept of fixed mode, the stabilizability and pole assignability of the expanded system with overlapping decomposition which has a decentralized information structure are studied. And the relationships of closed loop properties between the expanded and unexpanded system are also studied. It is obtained that the necessary and sufficient condition of stabilizability of expanded system is that the unexpancled system has no unstable fixed modes, while the necessary and sufficient condition of pole assignability of expanded system is that the unexpanded system has no fixed modes.