The invention discloses a hybrid switching system theory-based Buck circuit modeling method and application thereof. The method comprises the following working steps of: 1, analyzing a Buck circuit, portioning a state space, and determining the number of working states; 2, determining switching conditions among the working states; 3, establishing a sate equation and an output equation of the Buck circuit; 4, determining a state matrix, an input matrix and an output matrix of a system according to circuit parameters; and 5, establishing a model of the Buck circuit based on the hybrid switching system theory. By utilizing the hybrid switching system theory, the modeling of the Buck circuit is accurate, and system stability and control performance are accurately analyzed, particularly complicated characteristics of a converter system caused by switching; and the Buck circuit has the advantages of simple structure, small volume, high conversion efficiency and the like.