In this paper, the CCD-based microscopic measuring system is designed and produced to make measure of geometrical error of precision micropart, e.g. dimension, shape and location errors. The system consists of the tool maker's microscope with the CCD camera, the image acquiring board and the PC processing digital image. The algonthm and software used for computer digit image processing are discussed, e.g. establishing the threshold vale using the maximum variance method, two-valuing the image, removing the noise of the image and drawing the edges. The calibration of system is introduced and the measuring error of the system is analyzed. The practical measuring example is given. The experiment results in the conclusion that the system has come to practical use in measuring dimension error, coaxial one and roundness one of the precision microparts; its resolution is 0. 1 m; its repeatability is less than 0.5m. It is pointed that the better optical microscopic amplifying system and the CCD camera with higher resolution will make the measurement of the system more accurate, and the further perfection of algorithm and software will result in the system having more functions.