Abstract: Due to the limited room reserved for the loose side of the conveying chain in the carton conveying system in Changsha Cigarette Factory, it hinders the chain from free running when the chain becomes slack by wearing. As a solution to this problem, a preventive maintenance method was proposed as following:1) Adding chain cleaning and lubricating device to keep the chain clean and well lubricated. 2) A device for monitoring motor running status was designed to inspect chain elongation and wear. 3) Installing a chain guide monitor to stop the machine timely in case the chain running off the guide or elongated seriously. 4) Adding a safety guard in place. The results showed that:the frequency of chain running off decreased from 26 times to zero per year, the working life of chain guide prolonged from 1 year to more than 2 years, and the maintenance work was also reduced.