Steel tape is a commonly used length-measuring tool, which needs to be verified before using. In this paper, a method based on image processing for steel tape verification, which replaces the traditional eye detection, is proposed. Firstly, the camera is calibrated to get the pixel equivalent. Secondly, the standard steel tape and steel tape to be measured are arranged side by side on the calibration table, and the image of the integral meter is collected by the CCD camera. Thirdly, the acquired image is divided into regions, then the fine regions are further divided, and the area where the integral meter scale line locates is selected by the frame. Finally, the coordinates of the scale line at the integral meter are extracted and calculated by the method of pixel traversal and gray center of gravity. The error of the steel tape can be obtained by multiplying the difference between them by the pixel equivalent. The verification process is efficient and the results are reliable. The resolution of the measurement system can reach 0.04 mm, which meets the requirements of the measurement task.