Abstract: In order to clarify the main harmful components in mainstream smoke of flue-cured tobacco leaves from different growing areas in China, we selected 266 flue-cured tobacco samples from 17 flue-cured tobacco-producing provinces (municipalities) and 36 representative areas, and studied the differences of the main harmful components in mainstream smoke of flue-cured tobacco leaves between different areas and leaf positions, and variations of the same variety between different growing areas, leaf positions and years. The results showed that there were some variations of the main harmful components in mainstream smoke of flue-cured tobacco in China, of which, the coefficients of variation of NNK, ammonia and phenol were larger, those of benzopyrene and hydrogen cyanide were medium, and those of tar and crotonaldehyde were smaller. The differences in contents of tar, crotonaldehyde, NNK, ammonia, hydrogen cyanide and phenol in mainstream smoke of flue-cured tobacco leaves between different growing areas were significant, while the differences in carbon monoxide and benzopyrene were not significant. The differences in contents of tar, phenol, croton aldehyde, ammonia and NNK of mainstream smoke of flue-cured tobacco leaves between different leaf positions were significant, while the differences in carbon monoxide, benzopyrene and hydrogen cyanide were not significant. The variations of contents of hydrogen cyanide and NNK of flue-cured tobacco leaves between different growing areas were the highest, and the variation of content of phenol between different leaf positions was the highest. The variation of benzopyrene content between different leaf positions and between growing areas were higher than those between different years, and the variations of the contents of tar, carbon monoxide and crotonaldehyde between different leaf positions, growing areas and years were smaller.