Taking BuckBoost circuit as an example, the average model of the converter and its linearized smallsignal model were solved. Simulink software was used to build the equivalent circuits of state average equation and linearized smallsignal model respectively. By comparing the simulation results of dynamic model with those of switching device circuit, the correctness of the dynamic model was verified. The application scope and shortcomings of discontinuous current mode (DCM) average model were discussed. The theoretical analysis results showed that the largesignal model and the smallsignal model could better simulate the dynamic characteristics of the actual switching circuit on the macroscopic time scale. The smallsignal model could only be used to solve the case of small disturbances, namely when the disturbance was too large, the error of the smallsignal model solution would be large.