Abstract: In order to study the influences of microwave expanded cut stems on the reduction of harmful components in mainstream cigarette smoke, the effects of blending ratio of microwave expanded cut stems in cigarette on the deliveries of seven harmful components(CO, HCN, NNK, NH3, BaP, phenol and crotonaldehyde)in mainstream smoke and hazard index of cigarette were investigated and compared with those blended with pneumatically dried cut stems at the same blending ratio. The results showed that:Within the blending ratio of 8%-33%, microwave expanded cut stems performed better in reducing CO,HCN, BaP and crotonaldehyde in mainstream cigarette smoke with the average reduction amount of 1.0mg/cig, 9.43 μg/cig, 0.19 ng/cig and 0.42 μg/cig, respectively; while pneumatically dried cut stems were better in reducing NNK, NH3 and phenol in mainstream cigarette smoke with the average reduction amount of 0.12 ng/cig, 0.7 μg/cig and 0.23 μg/cig, respectively. Viewing from the hazard index of cigarette,the cigarette blended with microwave expanded cut stems was slightly better than that blended with pneumatically dried cut stems with hazard index 0.1 point less.