To　enhance　the　running　and　jumping　abilities　of　legged　robots　in　unstructured　environments,　joint　actuators　must　have　high　impact　resistance　for　high　torque　transmission.　A　cycloid-pin　gear　transmission　is　applied　in　joint　actuators　to　resist　the　instantaneous　impact　of　the　legged　robots.　In　order　to　study　the　impact　performance　of　the　transmission,　the　impact　force　model　of　the　gear　meshing　pair　was　proposed　based　on　H-C　contact　collision　model.　The　transient　dynamics　module　in　Ansys　Workbench　was　used　to　verify　the　correctness　of　the　meshing　impact　model.　Then　the　influence　of　eccentricity　and　equidistance　modification　on　meshing　impact　forces　were　studied.　It　is　shown　that　eccentricity　is　the　main　parameter　affecting　the　impact　performance　of　gear　meshing.　The　result　provides　a　design　method　to　enhance　the　impact　resistance　of　cycloidal　reducer,　and　is　of　great　significance　for　improving　the　fast　motion　ability　of　legged　robots.　©　The　Author(s),　under　exclusive　license　to　Springer　Nature　Singapore　Pte　Ltd　2023.