The invention relates to the technical field of online quality detection of automatic production process and discloses a method for grading adhesive bulk agricultural products on line. The method comprises the following steps of: 1, establishing a normalized moment inertia (NMI) characteristic model and a weighting rotary inertia standard deviation model for qualified bulk agricultural products; and 2, grading bulk agricultural products to be graded on line by utilizing the NMI characteristic model and the weighting rotary inertia standard deviation model of the qualified bulk agricultural products and NMI characteristics and weighting rotary inertia standard deviation information of the bulk agricultural products to be graded. The NMI characteristics, the weighting rotary inertia standard deviation and a mathematical model are introduced into online grading of the bulk agricultural products, the adhesive bulk agricultural products are automatically and nondestructively cut according to the adhesion conditions of the bulk agricultural products on a production line by using the distance transformation and watershed method, and the adhesive bulk agricultural products are graded, so that the qualification rate is detected on line.