The high gain converter based on coupled inductance has a good application prospect in both new energy generation and DC microgrid. The operating principle of high gain Buck-Boost converter based on coupled inductance is analyzed, the switching flow diagram method is adopted to establish the converter model, and the steady state model and AC small signal model are derived in detail. The simulation results of Power SIMulation(PSIM) software on the converter small signal model prove the correctness of the proposed model. The results of this paper have high reference value for the design of control circuit of high gain DC/DC converter.