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Mature rapeseed pods split easily. Under the shearing and vibration forces of the side knife, the pod splits, and the rapeseed scatters out of the header, resulting in high rapeseed losses. Aiming at the problem, side knife cutting scattered seed pneumatic recovery method was proposed, and positive and negative pressure combined side knife cutting scattered seed recovery device was designed. The scattered materials were collected by the positive pressure airflow direction and transported to the entrance of the negative pressure airflow, and then directed by the negative pressure airflow to recover and pneumatically transported back to the header to achieve recovery and loss reduction. The internal flow field simulation analysis model of the recycling tube was built based on Fluent. The results of the single-factor test showed that the negative pressure airflow velocity was decreased with the increase of the throat diameter and increased with the increase of the throat inclination angle, and the diameter and inclination angle of the throat were determined to be 70mm and 120° respectively. Negative pressure airflow velocity was decreased with the increase of decreasing angle and decreasing angle in a certain range and there was an interactive effect, the determining factors were the inlet diameter, shrinkage length, outlet diameter and diffusion length. A quadratic regression orthogonal combination test was conducted using negative pressure airflow velocity as the evaluation index. The results showed that the importance of the factors affecting the negative pressure airflow velocity were length of the diffusion length, inlet diameter, shrinkage length, and outlet diameter. The optimized parameter combination was inlet diameter of 94mm, shrinkage length of 38mm, outlet diameter of 115mm and diffusion length of 350mm. A coupled CFD-DEM simulation model of the internal airflow-material in the recovery device was developed to study the influence of positive and negative pressure airflow velocity on the material recovery effect. The results showed that the material recovery rate was firstly increased and then decreased with the increase of positive pressure airflow velocity, and continued to increase with the increase of negative pressure airflow velocity. The optimal positive pressure airflow velocity was determined to be 20m/s. Based on the analysis of positive and negative airflow, the ratio of the cross-sectional area of the two airflow channels in the airflow distributor was determined to be 1∶3. Field tests showed that the loss rate of rapeseed header and side knife were 1.26% and 0.39% respectively after equipping scattered seed recovery device, and the loss rate was decreased by 21.8% and 47.3% respectively. The header loss and side knife loss were effectively reduced. The study can provide a reference for the design of low loss rapeseed header.