R-theta　robot　arm　is　an　important　part　of　the　robot　to　achieve　the　function,　low　stiffness　seriously　affect　the　accuracy　and　efficiency　of　work,　so　the　requirement　of　stiffness　is　higher.　In　order　to　improve　the　rigidity,　this　paper　put　the　arm　structure　as　the　research　object　to　optimize.　First　of　all,　the　relationship　between　the　total　deformation　of　the　joint　arms　and　the　wall　thickness　of　the　arms　are　analyzed,　get　the　optimal　wall　thickness　and　improving　the　structure　of　the　arm,　a　new　arm　structure　model　is　established.　On　this　basis,　the　topology　optimization　method　based　on　homogenization　method　is　used　to　optimize　the　arm　structure　and　get　the　final　optimal　structure.　Finally,　verification　and　analysis　are　carried　out　on　the　arms　of　a　single-arm　R-theta　robot.　The　results　show　that　the　combination　of　two　optimization　methods　can　not　only　effectively　reduce　the　arm　weight,　but　also　better　improve　the　natural　frequency,　thereby　increasing　the　stiffness　The　model　and　analysis　conclusion　of　this　paper　will　provide　theoretical　support　for　the　actual　improvement　of　the　motion　performance　of　the　robot.