Abstract: In order to analyze the genetic mechanisms of harmful components in mainstream cigarette smoke, the recombinant inbred lines (RIL) crossed by flue-cured tobaccos Y3 and K326 were used in the major gene plus polygene mixed genetic model method analyses for Carbon Monoxide (CO), Hydrocyanic acid (HCN), 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK:), Ammonia (NH₃), Benzoapyrene (BaP), Phenol (PHE), Crotonaldehyde (CRO) and Tar (TAR) in three consecutive generations (2018F_6:7, 2019F_7:8 and 2020F_8:9). The main results were as follows: (1) The 8 traits value of RIL populations in three generations all showed normal or partial normal distribution of single or multi peaks, belonging to typical quantitative inheritance. (2) The optimal genetic models for the 8 traits were all controlled by four major genes with partially equally additive (PEA) effects inheritance in three consecutive years. The optimal genetic model of CO, HCN, NNK, NH₃, BaP and CRO was 4MG-EEA, controlled by four major genes with partially equally additive 1 (PEA1) effect mixed inheritance; The optimal genetic model of PHE and TAR was 4MG-EEEA, controlled by four major-genes with partially equally additive 2 (PEA2) effect mixed inheritance.(3) These typical harmful components in mainstream cigarette smoke were only controlled by the major gene genetic model in 3 generations, and the heritability of the main genes was higher than 85% (mean 89.01%) and much greater than that of the environmental effect. In conclusion, these traits are mainly determined by genetic basis, which can provide theoretical basis for cultivating low-harm tobacco varieties.