In　addition　to　the　focusing　and　imaging　functions，Metalens　can　also　manipulate　light　field　polarization，wavelength，and　amplitude　through　kinds　of　meta-units.　Due　to　the　small　size，light　weight，low　cost　and　easy　inte⁃　gration，Metalens　has　become　a　research　hotspot　and　important　trend　in　optoelectronic　integration　area.　In　this　pa⁃　per，finite-difference　time-domain（FDTD）algorithm　is　used　to　design　and　optimize　Metalens　based　on　in⁃situ　inte⁃　gration　of　InGaAs　avalanche　detectors，and　the　focusing　efficiency　and　transmittance　of　the　Metalens　are　calculated.　The　simulation　results　show　that　the　Metalens　converges　incident　light　into　the　absorption　layer　of　detector，the　trans⁃　mittance　reaches　82.　8%，and　the　focusing　efficiency　reaches　84.　89%　when　the　target　focal　length　is　150　μm　and　the　Metalens　radius　is　50　μm.　To　further　increase　the　transmittance，an　anti-reflection（AR）layer　is　added.　The　results　show　that　the　maximum　transmittance　is　86.　6%　and　87.　6%　for　300　nm　SiO2　and　250　nm　SiN.　Compared　with　the　Metalens　without　AR　layer，the　max　transmittance　increased　by　3.　8%　and　4.　8%，respectively.　Finally，it　is　estimat⁃　ed　that　the　energy　of　the　light　field　in　the　absorption　region　integrated　with　Metalens　is　250.　96　times　higher　than　that　of　the　detector　without　Metalens，which　can　greatly　improve　the　responsivity　of　detector.　This　paper　proposes　a　mono⁃　lithic　integrated　method　for　avalanche　detector　with　Metalens，which　can　concentrate　the　energy　outside　the　detection　area　into　absorption　area，improves　the　quantum　efficiency　of　detector　without　bandwidth　reduction.　This　will　provide　a　new　sight　for　high　responsivity　and　high　bandwidth　detectors.　©　2023　Chines　Academy　of　Sciences.　All　rights　reserved.