Spin-polarized　two-dimensional　(2D)　materials　with　large　and　tunable　spin-splitting　energy　promise　the　field　of　2D　spintronics.　While　graphene　has　been　a　canonical　2D　material,　its　spin　properties　and　tunability　are　limited.　Here,　this　work　demonstrates　the　emergence　of　robust　spin-polarization　in　graphene　with　large　and　tunable　spin-splitting　energy　of　up　to　132　meV　at　zero　applied　magnetic　fields.　The　spin　polarization　is　induced　through　a　magnetic　exchange　interaction　between　graphene　and　the　underlying　ferrimagnetic　oxide　insulating　layer,　Tm3Fe5O12,　as　confirmed　by　its　X-ray　magnetic　circular　dichroism　(XMCD).　The　spin-splitting　energies　are　directly　measured　and　visualized　by　the　shift　in　their　Landau-fan　diagram　mapped　by　analyzing　the　measured　Shubnikov-de-Haas　(SdH)　oscillations　as　a　function　of　applied　electric　fields,　showing　consistent　fit　with　the　first-principles　and　machine　learning　calculations.　Further,　the　observed　spin-splitting　energies　can　be　tuned　over　a　broad　range　between　98　and　166　meV　by　field　cooling.　The　methods　and　results　are　applicable　to　other　2D　(magnetic)　materials　and　heterostructures,　and　offer　great　potential　for　developing　next-generation　spin　logic　and　memory　devices.　©　2023　The　Authors.　Advanced　Materials　published　by　Wiley-VCH　GmbH.