Abstract: A method to calibrate the relative position and orientation between robot and positioner was presented by fitting sphere based on the least square method. Firstly,the positioner rotates or tilts to different positions,and the position data of TCP were recorded in the same time. The optimal sphere was fitted by the least square method,and the origin of base coordinate frame of the positioner was calculated. Secondly,several points were recorded in the same way to calculate the vectors of axis. In order to avoid the effects of causal factors,the concept of deviation rate was presented to verify the accuracy of the marked points. Experiments show that this method can reduce the random error and avoid the effects of causal factors,which has high precision.