Abstract: According to the adjoint transformation relationship between the theoretical and actual values of joint twists in the product of exponential (POE) formula, the robot's kinematics equation is transformed into an equivalent form including the joint constraints. The linearized equation describing the relationship between the positioning errors of the end-link and the errors in the joint twists and in the zero position is obtained by differentiating the kinematic equation. With the definition of distance accuracy, the robot's distance error model is set up in POE form, which can avoid the coordinate transformation error from measurement equipment coordinate system to robot's base coordinate system. A kinematic calibration model of robots is presented based on the least-squares method. Finally, a kinematic parameters calibration experiment of a 5-DOF (degree of freedom) manipulator is completed with the help of a laser tracker. The testing result shows that the mean value of the distance errors of the robot is reduced about 3.5 times on the testing points generated randomly after parameter calibration.