Two-dimensional　(2D)　van　der　Waals　heterostructure　(vdWH)-based　floating　gate　devices　show　great　potential　for　next-generation　nonvolatile　and　multilevel　data　storage　memory.　However,　high　program　voltage　induced　substantial　energy　consumption,　which　is　one　of　the　primary　concerns,　hinders　their　applications　in　low-energy-consumption　artificial　synapses　for　neuromorphic　computing.　In　this　study,　we　demonstrate　a　three-terminal　floating　gate　device　based　on　the　vdWH　of　tin　disulfide　(SnS2),　hexagonal　boron　nitride　(h-BN),　and　few-layer　graphene.　The　large　electron　affinity　of　SnS2　facilitates　a　significant　reduction　in　the　program　voltage　of　the　device　by　lowering　the　hole-injection　barrier　across　h-BN.　Our　floating　gate　device,　as　a　nonvolatile　multilevel　electronic　memory,　exhibits　large　on/off　current　ratio　(similar　to　10(5)),　good　retention　(over　10(4)　s),　and　robust　endurance　(over　1000　cycles).　Moreover,　it　can　function　as　an　artificial　synapse　to　emulate　basic　synaptic　functions.　Further,　low　energy　consumption　down　to　similar　to　7　picojoule　(pJ)　can　be　achieved　owing　to　the　small　program　voltage.　High　linearity　(＜1)　and　conductance　ratio　(similar　to　80)　in　long-term　potentiation　and　depression　(LTP/LTD)　further　contribute　to　the　high　pattern　recognition　accuracy　(similar　to　90%)　in　artificial　neural　network　simulation.　The　proposed　device　with　attentive　band　engineering　can　promote　the　future　development　of　energy-efficient　memory　and　neuromorphic　devices.