Abstract: In considering of the dimension enlarge problem which emerges in solving process of decentralized LQG control systems on algorithm combining time-scale seperation and decentralized structure is presented.This algorithm converts the high-order system problem into low-order system ones for obtaining solutions.It is possible to calculate the guasi optimal solutions for arbitrary decentralized information structure systems.By calculating a power system model,the state estimation and feedback law with decentralized structure,linear and finite dimension are obtained.