This paper presents a non-isolated three-port switching boost converter and applies it to photovoltaic systems. The topology combines the characteristics of the switching boost network. By controlling three degrees of freedom, the ports have boost, buck, and buck-boost characteristics. It expands the three-port converter (TPC) working range with the advantages of simple structure, small size, and low cost. The operating mode and power flow direction of the TPC are determined according to the state of charge (SOC) of the energy storage system. Analyses of the working state of the topology in different working modes further verify the power flow of the system and explain its control strategy to complete the smooth switching of different working modes. Finally, the correctness of the above theory and its feasibility in photovoltaic system are verified by simulation and experiment.