Abstract: 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.