Gelidium　amansii　(GA)　is　a　kind　of　red　alga　homologous　to　medicine　and　food　and　is　distributed　all　over　the　world.　Studies　on　GA　are　mainly　focused　on　its　polysaccharides,　with　little　research　on　the　ethanol　extract.　The　ethanol　extract　of　Gelidium　amansii　(GAE)　was　subjected　to　a　reverse-phase　column　to　obtain　7　components.　Among　them,　100%　methanol　solution　(GAM),　enriched　with　phytene-1,2-diol,　exhibited　the　strongest　DPPH　free　radical　scavenging　activity　(IC50　=　0.17　mg　mL−1).　Subsequently,　high-fat　male　flies　(HMFs)　were　used　as　a　model　to　explore　the　antioxidant　and　anti-aging　effects　of　GAM　in　vivo.　Studies　showed　that　GAM　can　effectively　prolong　the　lifespan　of　HMFs.　When　GAM　concentrations　were　0.2　and　1.0　mg　mL−1,　the　average　lifespan　of　HMFs　was　increased　by　28.7　and　40.7%,　respectively,　while　the　longest　lifespan　of　HMFs　was　increased　by　20.55%　and　32.88%,　respectively.　Further　research　revealed　that　GAM　can　significantly　downregulate　the　levels　of　malondialdehyde　(MDA)　and　protein　carbonyl　(PCO),　and　can　significantly　upregulate　the　levels　of　catalase　(CAT)　and　total　superoxide　dismutase　(T-SOD).　In　addition,　by　analyzing　differential　metabolites,　we　found　that　GAM　relieves　aging　caused　by　oxidative　stress　by　regulating　amino　acid,　lipid,　sugar,　and　energy　metabolism.　The　GAM　group　significantly　regulated　the　levels　of　adenine,　cholic　acid,　glutamate,　l-proline,　niacin,　and　stachyose　which　tend　to　recover　to　the　levels　of　the　normal　diet　male　fly　(NMF)　group.　In　general,　our　research　provides　ideas　for　the　high-value　utilization　of　GA　and　provides　a　lead　compound　for　the　research　and　development　of　anti-aging　food　or　medicine.　©　2022　The　Royal　Society　of　Chemistry.