Cycloid　pinwheel　reducers　are　widely　applied　in　the　joint　parts　for　industrial　robots　with　their　characteristics　of　the　compacted　structure,　long　service　life,　and　strong　bearing　capacity.　However,　it　may　operate　with　various　friction　losses　in　application,　which　lead　to　the　decreasing　of　transmission　efficiency.　In　this　study,　the　transmission　efficiency　for　the　CT-CHR　type　cycloid　pinwheel　reducer　considering　friction　loss　is　modeled　with　multi-tooth　contact　analysis.　The　friction　losses　comprised　of　gear　meshing,　pin　dowel　output,　bearing　rotation,　sealing　element　and　lubrication　were　generalized　investigated,　the　influence　of　reducer　structure　parameters　on　factors　of　efficiency　and　maximum　meshing　force　were　systematically　analyzed　and　discussed.　The　multi-objective　optimization　based　on　genetic　algorithm　was　performed　on　cycloidal　reducer　mechanism　with　selecting　the　transmission　efficiency,　maximum　meshing　force,　total　volume　as　objectives,　and　structure　parameters　as　design　variables　with　corresponding　constraints.　The　solid　models　for　cycloid　pinwheel　reducer　before　and　after　optimization　were　established　and　compared,　and　the　finite　element　simulation　analysis　for　contact　stress　was　carried　out　for　verifying　the　correctness　and　feasible　of　theoretical　optimization　model.　The　results　illustrate　that　the　overall　performance　for　cycloid　pinwheel　reducer　can　be　effectively　improved　by　optimized　design.　This　study　can　provide　the　novel　design　ideas　for　the　designers　to　optimize　the　mechanical　components　in　field　of　industrial　engineering,　which　has　the　certain　academic　value　for　the　guideline　and　reference　of　optimization　design.