In view of the problems of small shape difference, large degree of mixture, and difficulty in sorting the flax exudate after segmented harvesting, a flax threshing sorting device was designed. In order to improve the operation efficiency of the flax threshing sorting device, the mechanism of airflow cleaning of flax threshing materials was explored, and the CFD model of the cleaning system and the DEM model of flax detachment were established with the airflow sorting system of the device as the research object. Using CFD-DEM coupling simulation technology, the separation law of flax exudate in the sorting system was obtained by studying the motion trajectory and spatial position distribution of the detached materials of each component, and verification tests were carried out to verify the reliability of the simulation model. The simulation test showed that the flax threshing particles showed a good separation and sorting effect under the action of the air flow field in the cleaning system, and at the same time, the variation curve of the number and average velocity of flax threshing particles obtained by the simulation test was analyzed, and the change law of the average speed and quantity of flax threshing materials in the process of separation and sorting was detected. The verification test showed that the removal loss rate of flax grain after operation under the best working condition of the device was 2.78%, and the impurity rate was 2.23%, which was only 0.73 and 0.67 percentage points different from the simulated flax grain loss rate (2.05%) and impurity content rate (1.56%), respectively, and the actual test results were in high agreement with the simulation results, which verified the reliability of the model.