The work aims to design an online stem separation system to solve the problems that the original stem of the ZJ17 cigarette machine cannot be separated completely and the cut tobacco rate in the stem is high. Through the research on the system's vacuum suspension device, centrifugal air dividing device and air dividing speed, the secondary air dividing of tobacco stem was realized, and a better separation and recovery effect of tobacco stem was achieved. At the same time, through human-computer interaction, automatic control of air diving pressure and stem flow was realized to ensure the separation effect and stability of system operation. The stem separation system could realize the online separation and recovery of the stem and the automatic regulation of air diving pressure, and reduce the cut tobacco rate in the stem mixture from 20.33% to 1.8%. The system can effectively improve the utilization rate of cut tobacco and reduce the consumption of tobacco. The system can be promoted and applied to all ZJ17, ZJ118 and other cigarette machines in the industry.