The system was based on the differenceof X-ray absorption capacity of different density materials to design On-line elimination system of foreign materials in cut tobacco based on X-ray. The system uses X-ray to transmit the cut tobacco to form the original density data, and uses the mutation of the original density value to distinguish the foreign materials, so as to realize the function of on-line detection and recognition of foreign materials. And a unique method of screening out foreign materials by parallelogram injection which made the foreign materials close to the center of the parallelogram was designed to improve the effectiveness of screening out the foreign materials in cut tobacco. The experimental results showed that the device could effectively identify and eliminate all kinds of metallic and non-metallic foreign materials when it was installed at the outlet of cut tobacco cabinet of primary processing line. The average recognition rate of foreign materials in cut tobacco is above 99.5%, and the average elimination rate is above 95.8%.