Aiming at the problems of low efficiency and insufficient positioning accuracy in traditional sub-pixel edge detection methods, this paper proposes a sub-pixel edge detection algorithm based on Prewitt operator and Franklin moment fusion. Firstly, the Prewitt operator is used to realize the pixel-level initial positioning of the edge, and then the sub-pixel edge analysis model based on Franklin moment is constructed. The multi-order moment convolution is used to extract the edge features. Combined with the orthogonality and rotation invariance of the moment function, the relationship between the moment values before and after the image rotation is established, so as to accurately calculate the sub-pixel coordinates of the edge points, and the effective screening of the edge points is completed by the improved discriminant conditions. Finally, the least square method is used to fit the edge. The experimental results show that the average error of the jet port detection is 0.002 6 mm, the average detection time is 0.805 s, and the positioning accuracy is higher, the noise resistance is stronger, and the universality is better. It can better solve the problems of low positioning accuracy and slow efficiency of image edge detection.