An improved fast global sliding mode control is proposed to overcome the disadvantage that the dynamic sliding mode surface of the conventional global sliding mode control cannot evolve into the linear sliding mode surface in a limited time. The attenuation function of the dynamic sliding mode surface is differentiable and composed of three exponential functions which can decay to zero in a limited time. Thus, the method not only is strong global robustness, but also evolves the dynamic sliding mode surface into the linear sliding mode surface in a limited time. In this way, the response rate of the system controlled can be accelerated by using the method. The method is used to control the chaos in the second order power system. Simulation results show the effectiveness of the proposed method.