This paper is concerned with the Decentralized Control of the dynamic behaviour of the Complex Power System (CPS). It is suggested here two different approaches for designing Suboptimal Decentralized Controllers by using the Modified Bellman-Lyapunoff Equation(MBLE) via the optimal techniques. In the first approach, Suboptimal Control Laws for turbine powers are deduced by the aid of scalar Lyapunoff Function(LF) for the whole system. In the second one, Suboptimal Control Laws are deduced with the aid of using vector LF which can be constructed by decomposing the power system to some interconnected subsystems.