In order to deeply understand the internal unsteady flows in vortex pumps, based on the RNG k-ε turbulence model, numerical simulation of unsteady flows was carried out to analyze the vortex cores, turbulent kinetic energy distribution and internal pressure pulsation in different fluid domains of vortex pumps under three flow rates by CFX. The results show that the vortex cores of the inlet pipeline gradually decrease with increasing flow rates. The diameter and flow velocity of the circular vortex band connected end to end in the inner ring increases within the volute, and the vortex cores in the outer ring gradually disperse within the volute. The size of the vortex cores in the transition region of the diffuser tube and at the volute tongue increases significantly. Under low flow and rated flow conditions, the high-brightness turbulent kinetic energy is concentrated in the inner ring of the volute, and the main frequency of the internal pressure pulsation is the rotational frequency of the blade. Under large flow conditions, the high-brightness turbulent kinetic energy is concentrated in the transition area from the volute to the diffuser, and the main frequency is the rotational frequency of the axis. The non-vortex core area in the impeller is mostly concentrated in the upstream surface of the blade. With the increase of the flow rate, the vortex core distribution gradually disperses, and the non-core area increases. The high-brightness turbulent kinetic energy is distributed at the blade inlet under low flow, in the middle of flow channel under rated flow, and at the blade outlet under large flow. The main frequency of the pressure pulsation in the blade flow channel is always the rotational frequency of the axis.