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The hydrogen pump is an important component in the hydrogen circulation system of fuel cells. Excessive pulsation at the outlet of the pump is challenging when the Roots hydrogen pump is used, which has a negative impact on the operation performance. To reduce the impact of excessive fluctuations in the hydrogen circulation system, a new structure of reflow grooves is proposed in this paper, which connects the different chambers and adjusts the pressure using a diversion method. The internal flow of the two pumps was studied for comparison, using a three-dimensional simulation model established by Computational Fluid Dynamics (CFD) method. Results showed that the reflow grooves reduce the exhaust pressure and mass flow pulsations, which has a positive effect on the pressure stabilization of the hydrogen circulation system and the anode inlet pressure of the fuel cell stack, contributing to the long durability and stability of the fuel cell stack. [Display omitted] • A novel reflow structure is proposed for the Roots hydrogen pump. • The internal flow of the pump is simulated by the dynamic grid method. • The gas pressure variation in one compression in the Roots pump was analysed. • The reductions in flow fluctuations at different rotational speeds are compared. • Pressure fluctuation is supressed at high rotation speed by the reflow structure. [ABSTRACT FROM AUTHOR]