Based　on　the　H-C　contact　collision　model　and　the　Hertz　contact　collision　deformation　law,　the　meshing-in　impact　force　model　and　analysis　method　considering　cycloid　gear　tooth　profile　modification　parameters　and　mechanism　design　parameters　was　proposed　in　the　paper　with　a　view　to　solving　the　problems　such　as　sudden　change　of　transmission　error　and　increased　vibration　impact　in　RV　reducers　caused　by　off-line　meshing-in　impact　due　to　the　existence　of　clearance　in　the　cycloid-pin　gear　drive　mechanism.　Firstly,　based　on　the　mechanism　of　how　off-line　meshing-in　impact　happened,　the　theoretical　meshing-in　point　and　the　actual　meshing-in　point　were　determined　and　the　calculation　method　of　elastic　torsion　angle　was　clarified.　Secondly,　based　on　the　HC　contact　collision　model　and　the　Hertz　contact　collision　deformation　law,　the　meshing-in　impact　force　model　of　the　cycloid-pin　gear　drive　mechanism　considering　damping　force　was　proposed.　Then,　by　using　the　multivariate　fitting　method,　the　mapping　relationship　between　the　design　pa　rameters　such　as　cycloid　gear　radial-moving　modification　and　eccentricity　and　the　meshing-in　impact　force　was　constructed,　and　the　influence　mechanism　of　the　off-line　meshing-in　impact　characteristics　of　the　cycloid-pin　gear　drive　mechanism　was　revealed.　Finally,the　Ansys　transient　dynamics　module　was　used　to　simulate　the　collision　dynamic　force　of　the　cycloid-pin　gear　drive　mechanism.　The　results　show　that　the　meshing-in　impact　force　increases　with　the　decrease　of　the　negative　radial-moving　modification　amount,　the　increase　of　the　positive　radial-moving　modification　amount　and　the　decrease　of　the　eccentricity；　the　maximum　impact　force　error　between　theory　and　simulation　result　is　7.　98%,　which　is　in　the　allowable　range　and　proves　the　feasibility　of　the　off-line　meshing-in　impact　model.　The　research　results　can　provide　a　theoretical　basis　for　the　design　and　optimization　of　the　cycloid-pin　gear　drive　mechanism　of　RV　reducers.　©　2023　Xi＇an　Jiaotong　University.　All　rights　reserved.