Over　the　past　several　years,　there　has　been　a　substantial　surge　in　the　utilization　of　metasurfaces　in　microelectronics　and　micro-optical　devices.　As　one　of　their　applications,　metalenses　have　aroused　significant　research　interest.　In　this　paper,　a　new　optimization　method　based　on　micro　co-fluctuation　model　is　proposed　to　optimize　the　initial　metalens　for　better　focusing　performance　by　adjusting　the　structural　dimensions　of　nanopillars.　A　segmenting　iteration　strategy　is　used　to　legitimately　reduce　the　computation　space.　Meanwhile,　an　improved　Harris　Hawks　Optimizer　(IHHO)　is　proposed　to　obtain　the　optimal　solutions,　in　which　a　new　formula　for　escape　energy　is　defined　to　promote　the　diversity　of　solution　space.　The　optimization　results　indicate　that　the　proposed　optimization　method　effectively　enhances　the　focusing　capability　of　the　initial　metalens　with　a　numerical　aperture　(NA)　of　about　0.7　and　an　operating　wavelength　of　10.6　&　mu;m.　The　maximum　field　intensity　of　the　central　hot　spot　and　the　absolute　efficiency　have　increased　by　approximately　59.02%　and　71.13%,　respectively,　and　the　full　width　at　half　maximum　(FWHM)　remains　nearly　the　same　value,　which　provides　the　potential　for　achieving　high-contrast　imaging.