The input-parallel output-parallel(IPOP) buck topology is used in electric vehicle charging and data center power supply due to its ability to provide low voltage and high current outputs. However, a serious problem with the IPOP buck is the circulating current between the modules, which affects the reliability of the power supply. This paper focuses on the circulating current in IPOP buck and proposes a control strategy for IPOP system. Firstly, the path of circulating current is analyzed based on the switching state, and then the influencing factors of circulating current are quantitatively analyzed. Secondly, a control strategy that not only enables average current sharing but also eliminates circulating currents is proposed in this paper. In addition, carriers are interleaved between modules to reduce output current ripple, which in turn reduces filter inductor size and improves power density. Simulation model of four IPOP bucks in MATLAB/Simulink as well as a 300W buck lab prototype demonstrate that the control strategy can evenly distribute power, suppress circulating currents, and reduce output current ripple.