Based on the three close-loop high precision position servo system, the error source is introduced and categorized into two errors. The one can be adjusted by the control algorithm and the other can not be adjusted by the control algorithm. The rounding error of computation, the measurement error of the sensor, the error of the sampling frequency, and the error from the bandwidth are analyzed quantitatively. The transmission and superposition of the error among the loops are analyzed according to the orders from the inner loop to the outer loop at the point of view of the physics kinematics. Through the quantitative analysis of the errors, the proportion of each error in the whole error is shown, which will provide important theoretic basis for the system design. The experiment is carried out and the theory of the error analysis is proved to be feasible.