In order to study the vortex pump flow field characteristics of its external, it is necessary to carry out unsteady flow numerical simulation by using RNG k—ε turbulence model and structured grid inside the vortex pump. The results showed that the pressure changes within the linear distribution, with flow rate increasing, longitudinal vortex flow decreased, while the radial vortex flow periodically was removed from the leaves and increased with time. The pressure fluctuation at the different monitoring points was changed periodically at design condition. The pressure pulse amplitude increased from the entrance to the exit gradually. The blade passing frequency was dominative in the pressure fluctuation. With the flow rate increasing, pressure fluctuation was more obvious under the blade passing frequency.