<p>In poppet valves under fully developed cavitation, cavitation develops in several distinct regions through different mechanisms. Moreover, complex interactions occur among cavitation structures and flow instabilities. Such phenomena should be carefully taken into account when developing cavitation suppression strategies of practical significance. Therefore, in the current study, a 3-D simulation is performed to investigate the cavitating jet through a traditional poppet valve with a chamfered valve seat, for the sake of clarifying the cavitation dynamics as well as relevant mechanisms. The transient process of cavitation reveals the interactive amalgamation between the cavitation and produced flow instabilities, particularly the collision of vortex cavitation into the collapsing large-scale cavities at wake. Therefore, the large-scale cavities beyond the poppet edge are persistently present throughout the whole cyclic process. Based on the governing mechanism of the cavitation dynamics, the current study proposes two structural optimizations to reduce cavitation intensity by eliminating the amalgamation process. On one hand, the location of both inlet and outlet corner point at each side of the groove prevents the direct contact of shed detached cavitation with the Kelvin-Helmholtz instability. On the other hand, the cylinder poppet as well as the parallel configuration elevates the flow divergence, substantially lowering the vortex cavitation and eliminating its amalgamation with large-scale cavities. The simulation result demonstrates that the time-average vapor content displays a reduction by over 28% under flow conditions with strong cavitation. The large-scale cavities in the proposed optimization display a significant reduction in collapse time as well as covering area. With such a method, the cavitation inception could even be induced with greater susceptibility. However, for fully developed cavitation, the cavitation region as well as vapor content is substantially suppressed.</p>