A power system is a typical nonlinear system. When the power system is subjected to periodic load disturbance, it is possible to induce chaotic oscillation as long as the amplitude of periodic load satisfies certain conditions. Chaotic oscillation in the power system may lead to voltage collapse, which seriously affects the stability and operation safety of the power system. In this paper, a feedback controller is designed for the fourth-order power system based on the theory of finite time stability. The numerical simulation results show that the controller proposed can effectively supress the chaos in the power system and has strong robustness to external disturbances and system parameters. When the exponential parameter of the designed control law is reduced, or any other control law parameters are increased, the time required for the system to recover to the target equilibrium state will be reduced.