Abstract: Oil leak was a problem of transfer arm in spider mechanism in PROTOS cigarette making machine,the leaked oil would enter the negative pressure passage and pollute cigarette.By analyzing the mechanism and causes of oil leak,the mechanism was improved as following:arranging a cavity between the oil chamber and negative pressure passage in transfer arm and a spiral labyrinth seal in front of bracket oil seal.After improving,the oil chamber was completely isolated from the negative pressure passage,the pressure difference between the two sides of bracket oil seal was reduced,and the possibility of oil leak was decreased.