With regard to the inter-area low-frequency oscillation problems in large-scale interconnected power system, a design method based on Fruit fly Optimization Algorithm (FOA) for the wide-area damping controller is proposed. The 16-machine 68-bus power system is employed to validate the effectiveness of the method presented. The system is linearized at first, and modal analysis is conducted to find out the interval oscillation modes and corresponding damping ratios, under which the rotor speed participation factors are obtained. Through the participation factors the wide-area feedback signal is selected appropriately. Afterwards, the structure of the wide-area controller is analyzed and the FOA algorithm is adopted to optimize the parameters. Finally, the simulation results show that the proposed design method of wide-area controller can better improve the inter-area oscillation damping ratios, which provides a new thought for the optimal control of low-frequency oscillation.