To improve the power quality of the multi-area interconnected power grid, a hybrid energy storage system (HESS) consisting of super capacitor and battery is applied to the traditional load frequency control(LFC) systems. In addition, an active fault-tolerant strategy is designed for the unavoidable sensor failure in power systems. To reduce the impact of disturbances on system frequency, the model of the LFC system with the HESS is established first. Then, an active fault-tolerant strategy is designed for the interconnected power system with the HESS to avoid system error caused by sensor fault. Finally, a three-area power system with the HESS is simulated to verify the feasibility of the HESS to improve the power quality of the interconnected system and the effectiveness of the proposed fault-tolerant control(FTC).