Fuel cells directly convert the energy stored in hydrogen into electrical energy through an electrochemical reaction, and the only reaction product is water, which can improve the energy efficiency and reduce the pollution caused by fossil fuels. The fuel cell hybrid power system used in vehicles usually consists of a fuel cell stack and a power battery module, and the DC/DC converter is the key component to connect them together. The current ripples caused by the system have been confirmed to have detrimental effects on the fuel cell’s reliability and lifespan. In addition, it is one of the key factors that reduce the system efficiency. So, it is necessary to analyze the current ripple in the system and maintain it at a low level. In this paper, a brief review on the different kinds of converters used in vehicles has been made. Then, with the help of MATLAB/SIMULINK, a simulation model of the hybrid power system based on 4-phase interleaved parallel topology is established. According to the feedback current, the designed model adopts the PI control method. After that, the paper proposes a Randles equivalent circuit model (ECM) to simulate the fuel cells’ volt-ampere characteristic, and the parameters of the circuit components are adjusted. Lastly, harmonic analysis is performed on the data of input and output current using the Fourier transform method, and the different orders harmonics of the input and output current are obtained. By comparing the amplitude of the harmonics, the optimal operating point of the converter could be obtained at which the current ripples are relatively small.