VO2　has　been　widely　used　in　optical　modulation　devices　due　to　its　large　change　in　permittivity　across　its　first-order　metal-semiconductor　phase　transition.　People　have　proved　that　VO2＇s　phase　transition　can　be　driven　by　plasmonic　hot-electron　injection,　providing　a　new　approach　to　realizing　ultrafast　all-optical　devices　with　a　low　pump　fluence.　Here,　we　report　on　ultrafast　VO2　all-optical　modulation　with　a　dramatically　low　pump　fluence　utilizing　the　composite　structure　of　a　self-supported　VO2　film　on　a　gold　nanoshell　grating.　Plasmonic　hot　electrons　in　the　gold　excited　by　femtosecond　pulses　are　injected　into　the　VO2　film　and　trigger　its　phase　transition,　reducing　the　pump　fluence　threshold　for　the　structural　transformation　to　only　147.8　mu　J/cm2.　With　a　pump　fluence　above　this　threshold,　ultrafast　phase　transition　can　be　triggered　within　1　ps,　and　a　high　modulation　depth　of　50%　can　be　achieved.　Moreover,　an　ultrafast　modulation　with　an　on-off　time　of　650　fs　can　also　be　achieved　using　a　pump　fluence　below　the　threshold.　This　work　may　explore　new　applications　of　plasmonic　hot-electron-driven　phase　transition　in　optical　modulation　devices　and　configurable　devices.