The　novel　concept　of　a　functionally　graded　three-phase　composite　structure　is　derived　from　the　urgent　need　to　improve　the　mechanical　properties　of　traditional　two-phase　composite　structures　in　aviation.　In　this　paper,　we　study　the　free　vibrations　of　a　new　functionally　graded　three-phase　composite　cylindrical　shell　reinforced　synergistically　with　graphene　platelets　and　carbon　fibers.　We　calculate　the　equivalent　elastic　properties　of　the　new　three-phase　composite　cylindrical　shell　using　the　Halpin-Tsai　and　Mori-Tanaka　models.　The　governing　equations　of　this　three-phase　composite　cylindrical　shell　are　derived　by　using　first-order　shear　deformation　theory　and　Hamilton＇s　principle.　We　obtain　the　natural　frequencies　and　mode　shapes　of　the　new　functionally　graded　three-phase　composite　cylindrical　shell　under　artificial　boundary　conditions.　By　comparing　the　results　of　this　paper　with　the　numerical　results　of　finite　element　software,　the　calculation　method　is　verified.　The　effects　of　the　boundary　spring　stiffness,　GPL　mass　fraction,　GPL　functionally　graded　distributions,　carbon　fiber　content,　and　the　carbon　fiber　layup　angle　on　the　free　vibrations　of　the　functionally　graded　three-phase　composite　cylindrical　shell　are　analyzed　in　depth.　The　conclusions　provide　a　certain　guiding　significance　for　the　future　application　of　this　new　three-phase　composite　structure　in　the　aerospace　and　engineering　fields.