With the aim to study the characteristics of complex vortices in the vortex pump, quantify the volume and intensity of vortices in pump, and analyze the influence of vortex structure on energy conversion and energy loss, the unsteady numerical simulation and external characteristic experiments were carried out to analyze the single-stage vortex pump, the Ω method, and Liutex method were used to identify and characterize the intensity of vortex in the pump, the average vortex intensity was proposed for the quantitative study, and the analysis was carried out by combining the vortex dynamics decomposition formula of kinetic energy equation and the vortex decomposition theory. The results showed that there was a spiral vortex structure in the fully developed vortex region of the pump, which flowed out from the impeller channel into the side channel. With the increase of flow rate, the number of vortex tubes was decreased and the vortex strength was decreased. With the increase of flow rate, the volume and intensity of the vortex in the impeller was decreased, while the relative change in the side channel was relatively small. The average vortex intensity in the impeller was much greater than that in the side channel under the same working conditions. Pressure gradient contributed the most to the kinetic energy conversion of fluid, and the proportion of momentum transport and dissipation loss caused by vortex structure was small, but the rigid vorticity, that was, the strength of vortex structure, was positively related to momentum transport, while the deformed vorticity was strongly related to the energy loss of enstrophy.