The high flexibility optical processing system based on the industrial robot can process large or complex work-pieces. But the positioning error characteristics of the industrial robot will cause the decrease of positioning ac-curacy during grinding, which leads to a lower processing efficiency and processing precision. This paper studies the method of decreasing positioning error, which is verified by simulation and optical processing experiments: Firstly, the positioning error of the polishing tool that fixed at the end of robot in the working area is measured in real-time by using an API T3 laser tracker, and the errors of dwell points are compensated. The measurement experimental results show that the positioning accuracy of the polishing tool meets the high-precision optical processing requirements with the compensation. The dwell time error and the removal error caused by the posi-tioning error before and after compensation are simulated, and the results show that after compensation, the removal error on 80% full aperture is reduced from 3.68% to 0.90%. At last, through the method of the position error compensation to replan the trajectory, the improvement of the processing efficiency and the accurate con-trol on grinding are verified by polishing experiments.