Currently, pixel-level edge detection algorithms are mostly used in the dimension vision measurement for shaft parts, which can hardly be adapted to the high-precision measurement requirements of industrial automation. In order to improve the measurement accuracy of shaft diameter of shaft parts, a dimensional measurement method for shaft parts based on improved Zernike moment is proposed. Firstly, Canny edge detection algorithm is used for rough positioning in shaft images to obtain pixel-level edges. Then, in accordance with the grayscale difference between the target and the background information of the image , a method for obtaining the optimal decision threshold of Zernike moment based on the multi-threshold Otsu method is proposed to obtain sub-pixel edges. Finally, an improved least square method to fit the edge line of shaft images based on edge point search is proposed to obtain the measurements of the shaft diameter. The experimental results show that, taking the measurement of bicycle rear axle diameter as an example, the proposed algorithm has better stability than the traditional Zernike moment method, and the relative error with the manual measurement is less than 0.011%. The measurement accuracy of the proposed method can meet the accuracy requirement of 6-level of bicycle axle diameter in industrial parts dimension measurement.