To　improve　the　control　accuracy　of　robot　tip,　according　to　the　Power　Cube　modular　robot　system,　the　real-time　position　feedback　control　method　based　on　the　Optotrak3020　motion　measurement　system　is　presented　and　the　complicated　trajectory　tracking　control　of　the　modular　robot　is　studied.　Power　Cube　modular　robot　system　structure,　measurement　of　joint　angle　error,　and　control　concept　and　structure　of　real-time　position　feedback　are　investigated,　respectively.　Then,　through　a　3D　simulation　and　experiment　of　the　modular　robot　arm　for　tracking　a　plane　circular　arc,　the　feasibility　and　validity　of　the　control　strategy　and　experimental　system　are　verified.