A peanut negative pressure grading device with simple structure, good grading effect and easy operation was designed based on Laval nozzle structure. Five factors affecting the vacuum degree in negative pressure tube were simulated and the structure size of air duct was determined based on Fluent. CFD-DEM coupled simulation software was used to simulate the negative pressure sorting of two kinds of peanuts with the same volume and small density difference, and the sorting differences of high quality and inferior grade peanuts were obtained. On this basis, taking the sorting height, conveyor belt speed and air inlet speed as experimental variables, the negative pressure grading experiment of peanut was carried out by setting up a negative pressure grading test bench. The experiment proves that the negative pressure sorting device based on Laval nozzle structure can complete the negative pressure sorting operation of peanuts.