Aiming at the low precision and heavy workload of manual measurement, as well as the high cost and complex operation of high-precision measuring instruments, a precision measuring instrument and method of fertilizer shape characteristics are proposed. In this method, the fertilizer shape characteristics are calculated by image acquisition, gray and gamma correction, and edge detection. Firstly, the measuring instrument works in an intermittent collection mode, which can acquire the top and side images of fertilizer at the same time. Secondly, gamma correction is performed on the top and side grayscale images to improve the image contrast, after the fertilizer image collection is completed. Finally, the edge detection algorithm based on the orientation gradient is proposed to extract the top and side contour images of the fertilizer accurately, and the shape characteristics are calculated from the contour images. The shape characteristics of the compound fertilizer, the organic fertilizer, and the biological fertilizer are measured by using the three-dimensional scanning method and the method proposed in this paper. The significant difference test between the two methods is evaluated by the Grubbs test, F test, and t test. The results show that there is no significant difference between the two measuring methods of fertilizer shape characteristics. The proposed measuring instrument and method proposed in this paper can quickly and accurately measure the fertilizer shape characteristics, which can lay a solid foundation for fertilizer production and quality inspection.