Abstract: To reject defective cigarettes accurately in ZJ118 and ZJ112 cigarette makers, the air circuit in final cut drum for foreign matter rejecting in ZJ112 cigarette maker was optimized with CREO parametrization design tools. On the premise of ensuring air distribution phase unchanged and air distribution outlets in alignment, the air circuit for front row cigarettes was changed into a linear passage similar to that for rear row cigarettes. The air circuits before and after improvement were tested with FluidSIM-P simulation software to promote the synchrony and sensitivity of air distribution in the final cut drum. Rejecting experiments were conducted with 120 foreign matters (rubber strips) containing cigarettes, the results showed that the rejection accuracy increased from 93.33% to 100% after improvement. The improved final cut drum was applied to ZJ112 and ZJ118 cigarette makers, the number of rejected cigarettes containing foreign matter reported per shift agreed with the practical statistical value, it indicated that all cigarettes containing foreign matter were rejected. The reliability of foreign matter rejection was promoted effectively.