©　2018　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim　Ferromagnetic　insulator　thin　film　nanostructures　are　becoming　the　key　component　of　the　state-of-the-art　spintronic　devices,　for　instance,　yttrium　iron　garnet　(YIG)　with　low　damping,　high　Curie　temperature,　and　high　resistivity　is　explored　into　many　spin–orbit　interactions　related　spintronic　devices.　Voltage　modulation　of　YIG,　with　great　practical/theoretical　significance,　thus　can　be　widely　applied　in　various　YIG-based　spintronics　effects.　Nevertheless,　to　manipulate　ferromagnetism　of　YIG　through　electric　field　(E-field),　instead　of　current,　in　an　energy　efficient　manner　is　essentially　challenging.　Here,　a　YIG/Cu/Pt　layered　nanostructure　with　a　weak　spin–orbit　coupling　interaction　is　fabricated,　and　then　the　interfacial　magnetism　of　the　Cu　and　YIG　is　modified　via　ionic　liquid　gating　method　significantly.　A　record-high　E-field-induced　ferromagnetic　resonance　field　shift　of　1400　Oe　is　achieved　in　YIG　(17　nm)/Cu　(5　nm)/Pt　(3　nm)/ionic　liquid/Au　capacitor　layered　nanostructures　with　a　small　voltage　bias　of　4.5　V.　The　giant　magnetoelectric　tunability　comes　from　voltage-induced　extra　ferromagnetic　ordering　in　Cu　layer,　confirmed　by　the　first-principle　calculation.　This　E-field　modulation　of　interfacial　magnetism　between　light　metal　and　magnetic　isolator　may　open　a　door　toward　compact,　high-performance,　and　energy-efficient　spintronic　devices.