In order to investigate the effect of the rotational speed on the internal flow and phase distribution in a multiphase pump, based on the twofluid model and the standard κ-ε turbulence model, Fluent software was used to carry out numerical calculation of threestage helicoaxial multiphase pump with different rotational speed under the design condition and the inlet gas void fraction was 30%. The results show that the effect of the rotational speed on the gas void fraction distribution in the first stage of the mixed pump was greater, and there is a difference in the effect trend between the pressure surface and the suction surface at different spans; the most obvious locations influenced by rotational speed on the gas void fraction are on the blade suction side at the span of 0.9; with the increase of the rotational speed, the vortex evolution in the diffuser is more obvious. The results can provide reference for the hydraulic design, and safe and stable operation of the multiphase pump.