The invention provides an automatic detection method for steel coil loosening, which comprises the following steps of acquiring depth data on the surface of a steel coil, denoising the depth data, andmapping a depth image into a grayscale image with the same size; carrying out image gradient detection on the gray-scale image by using a soft operator; carrying out connected domain analysis on theedge, and removing a noise area through a foreground pixel area; finding a gradient opposite point pair at the edge in an image edge region by utilizing the image gradient; and judging whether the roll is loosened or not by using the distance between the point pairs and combining depth information. The invention provides the automatic detection method for steel coil loosening, and the method is anon-statistical method, does not need a large amount of data annotation and long training time, saves a large amount of labor cost and time cost, and guarantees the robustness of a system to illumination by using the depth information.