Abstract: Accuracy of a manipulator is determined by its ability to position and orient its end-effector at the desired point in its workspace. It must be calibrated in order to improve its position accuracy. Kinematic model and the disturbance of exterior error are critical to the manipulator calibration. The effect of the manipulators′ initial orientation error on calibration was analyzed withdifferent kinematic model. A new mathematical model for manipulator calibration, which makes use of screw theory and distance error model, rather than conventional Denavit-Hartenberg(D-H) parameters and position error, was proposed. Based on the new model, the initial orientation errors of the manipulator were included thereinto. The nature drawbacks of D-H parameters in which small errors in theactual structure do not result in small changes in the kinematic parameters were avoided. The error resulting from the transformation between a measurement device frame system and a manipulator frame system was eliminated, and the difficulty in measurement technology could be overcome. Simulation was made to verify the correctness of the model.