In order to study vortex cavitation of jet flows, a compressible mathematical model of two-phase cavitation flows was built based on OpenFOAM open-source platform by using VOF algorithm. The three-dimensional dynamic simulation study of the cavitating jet inside a water poppet valve with sharp valve seat structure was performed, the instantaneous cavitation structure, pressure distribution and discharge coefficient were compared with the experimental data quantitatively or qualitatively and the flow characteristics were analyzed. The results show that the vortex cavitation is triggered in the free shearing layer of the jet flows, and the attached cavitation is formed at the trailing edge of the cone poppet; however, no cavitation phenomenon is observed in the wall boundary layer of the jet flows; the dynamic evolution of the free boundary layer cavitation structure is closely related to the dynamic characteristics of the vortex structure; the flow characteristic curve is generally stable and has a slight downward trend under cavitation; there is no pressure drop enough to trigger cavitation at the corner of the sharp valve seat, and the pressure decreasing gradient on the valve core surface is relatively flat, which provides a reasonable explanation for the smooth trend of vortex cavitation distribution and flow characteristic curve; the temporal evolution of cavitation structure indicates an obvious coupling between the vortex cavitation and adhesive cavitation at the back edge of the valve core. The results prove the flow dynamics of the cavitating jet inside a water poppet valve, and the cavitation inception mechanism and associated cavitation effect are explained from the basic level of hydrodynamics.