In order to solve the chaotic oscillation problem in power system, an adaptive sliding mode control method based on immersion invariance principle was proposed for the fractional order model of a six-order power system with energy storage device. Firstly, a six-order power system model with energy storage device was constructed and converted to fractional order, chaotic analysis methods such as bifurcation diagram are used to prove the existence of chaotic state in power system. Secondly, the chaos control of fractional order power system was divided to the chaos control of three subsystems, and the adaptive law of disturbance estimation and compensation term was obtained by designing the immersion invariance observer, the sliding mode surfaces and sliding mode functions were designed for the control objectives of different subsystems, thus an adaptive sliding mode controller with global fast performance was obtained. Finally, Lyapunov stability theory was used to prove the stability of closed loop system. The numerical simulation show that the controller can restore the chaotic power system to the equilibrium state and suppress the chaotic oscillation of the power system.