This　paper　reports　transient　dynamics　of　strong　near-field　coupling　behavior　of　plasmons　in　a　multilayer　metal　nanostructure　that　enables　ultrahigh-efficient　optical　switching.　Particle　plasmon　on　the　top　array　units　couples　with　localized/delocalized　plasmons　on　the　bottom　Au　film　to　produce　dipolar　and　high-order　hybrid　modes　with　nearly　suppressed　reflection.　The　mode　coupling　can　be　tuned　from　near-field　to　far-field　regime　readily　mediated　by　the　spacer　thickness.　The　dipolar　mode　inherits　the　high　dispersive　property　of　the　delocalized　plasmon,　but　the　higher-order　one　shows　limited　dispersion.　Transient　spectroscopy　illustrates　both　hybrid　modes　have　a　picosecond　timescale　redshift　under　on-　and　off-resonance　excitation.　However,　the　higher-order　mode　exhibits　a　longer　decay　lifetime　than　the　dipolar　one　because　of　resonance　characteristics　and　cavity　properties.　An　ultrafast　optical　switching　effect　with　a　response　time　of　tau　=　3.2　ps　and　an　ultrahigh　efficiency　of　5100　mOD　mJ-1　cm2　is　achieved　under　an　extremely　low　pump　fluence.　Transient　dynamics　of　strongly　coupled　plasmons　in　a　multilayer　metal　nanostructure　are　investigated　using　pump-probe　spectroscopy.　Particle　plasmon　has　strong　near-field　coupling　with　film　plasmons　to　produce　dipolar　and　high-order　hybrid　modes.　The　high-order　mode　decays　more　slowly　than　the　dipole　one　but　shows　a　similar　redshift　behavior　under　on-　and　off-resonance　excitation,　which　can　be　exploited　for　ultrafast　and　ultrahigh-efficient　optical　switching.　image