Aiming at the problem of the feasibility of the supposed self adjusting displacement equation when using the present method in the analysis of allowable errors for self adjustable mechanism with the mathematic approach of rotating vector, the authors establish the self adjusting displacement equation in the cylindrical pair, and calculate the self adjusting displacement to draw out the curve of the displacement by programming. The above results show that the suppose mentioned previously is feasible. Base on the equation established, an accurate method is used to determinate the allowable error angles which can make the mechanism realize self adjustment presented. By analyzing the results of the example, the method presented is proved to be correct and effective.