Abstract: To minimize the fluctuation of tobacco rod circumference and promote cigarette quality, an automatic tobacco rod circumference adjustment system was designed for ZJ116 cigarette maker. The original adjustment mechanism for the large pressing plate in the cigarette maker was modified and a cam mechanism was added to realtimely adjust the diameter of tobacco rod forming passage. In the modified adjustment mechanism, the linking rod, cover plate, fixed seat and a newly added swing arm form a four-linkage mechanism with self-locking function to stabilize the cover plate in the automatic adjustment process. In the cam mechanism, a servo motor controls the rotation of the cam according to the real-time tobacco rod circumference detected by the photoelectric circumference detector, and the cam drives the rotary plate and the large pressing plate to maintain the tobacco rod circumference within the setting range. The designed system was tested with "Honghe (hard 88)" cigarette brand in Honghe Cigarette Factory, and the results showed that the SD of cigarette circumference decreased from 0.059 to 0.050 mm, the rate of qualified cigarette increased from 98% to 100%, and the number of manual adjustment of large pressing plate was reduced from 5.4 times/shift to zero. This technology supports the promotion of cigarette quality.