To address high cleaning losses caused by high impurity content and uneven distribution during rapeseed threshing, this study proposes a drum pneumatic-assisted threshing and separation method. Initially, by determining the suspension velocity characteristics of various threshed components, auxiliary blades were designed and integrated to construct a non-uniform gradient airflow field, generating a directional pneumatic transport effect. CFD simulations confirmed that this configuration induces a stable axial spiral airflow. Driven dynamically by this airflow, miscellaneous materials are guided to migrate orderly toward the rear of the concave screen, enabling active source-based regulation of the spatial-temporal flow behavior and component distribution. Multi-parameter correlation analysis indicated a significant negative correlation (coefficient = –0.88) between axial airflow and the average impurity ratio. Field experiments demonstrated that at a feed rate of 2.8 kg/s with auxiliary blades, the grain loss rate was reduced to 3.7%, compared with 6.3% without auxiliary blades, corresponding to a 41.3% reduction. This research demonstrates that axial airflow can effectively regulate threshed material at the source, providing a novel approach for high-efficiency and low-loss threshing and cleaning.