In order to investigate the difference of the puff-by-puff release of nine major components (tar, nicotine, CO, NNK, B[a]P, phenol, crotonaldehyde, HCN and NH3) in mainstream smoke of slim and normal cigarettes, typical flue-cured cigarette samples from same cut tobacco were smoked by smoking machine under ISO. Results showed that: ① The average puffs of slim and normal cigarettes were 5.49 and 6.72 respectively, which showed there were significant statistical differences. In general, the puff-by-puff and total release of all components from slim cigarette were lower than from normal cigarette. and puff-by-puff release deviations of tar, nicotine, NNK, B[a]P, phenol, HCN and NH₃ in slim cigarette were smaller than normal cigarettes, while the law of CO and crotonaldehyde were opposite; ② With the proceeding of puffing, the puff-by-puff release of tar, nicotine, CO, NNK, B[a]P, phenol, HCN and NH₃ release per puff increased in both slim and normal cigarettes, except the crotonaldehyde release of the first puff; ③ The correlation trend between puff-by-puff yield of nine main components and puff number in normal cigarette were more significant than slim cigarette, while the factor of tar was controlled, the degree of change in correlation was opposite.