In this paper, the voltage regulation and transient stability of the multi-machine power systems are studied via decentralized switching controller. In most existing works, voltage and frequency stability of the multi-machine power systems are controlled by different controllers in different periods of power systems operation. The linearized model of the power system is established, and it takes both phase and voltage as parts of the feedback states. The switching controller is designed as an universalize robust controller in terms of linear matric inequality (LMI). The simulations are given to show that each generator can achieve transient stability and voltage regulation by implementing the proposed controller.