With the penetration of wind power in the power system constantly increasing, the uncertainty of its output poses a threat to the frequency stability of the system. Given this fluctuation problem of wind power connected to an interconnected power system, a variable universe fuzzy PI load frequency control strategy is proposed. To overcome the limitation in adaptive ability of the traditional fuzzy controller due to the fixed universe, a designed variable universe fuzzy PI load frequency controller realizes the dynamic adjustment of the input and output universes by the method of the variable universe. To satisfy the complex demands of universe adjustment after wind power is connected to the system, a new variable universe contraction-expansion factor based on fuzzy inference is designed. Simulation results of a typical two-area interconnected system show that the new controller has better control performance than the PI controller and the fuzzy PI controller under different forms of disturbance. It can better deal with the effect of the uncertainty of wind power output on the frequency stability of an interconnected power system. This work is supported by the Foundation of the Hebei Provincial Technology Support Program (No. 15212105D).