For a precise angle measurement positioning system, the existence of distortion may affect the geometric measurement accuracy directly. Therefore, the distortion of the optical system should be calibrated for its subsequent distortion correction. To solve the distortion calibration problem of a F-Theta optical lens, a calibration system based on the precise angle measurement method is established. The distortion calibration process is discussed in detail. The relation between the field of view and the absolute distortion is measured experimentally. The focal length of the F-Theta optical lens is derived by the least square approximation method based on curve fitting. Finally, the angle measurement accuracy of the F-Theta optical lens is analyzed. The result shows that the lens can meet the requirement of second-level angle measurement accuracy.