Abstract: Based on data of 14 chemical constituents and 2 physical parameters of 63 flue-cured tobacco samples, effect of 16 factors on CO yield behavior in mainstream smoke was investigated by correlation analysis and factor analysis. The result showed that wrapped density of rod and smoldering velocity of cigarette rod, crude fiber, nicotine, Cl, total ash and some metal elements such as K, Ca, Cu, Fe, had significant correlation (at 0.01 level) with CO yield behavior in mainstream. Six components were extracted by principal component analysis. F1(named fiber-burning component) had positive significant correlation (at 0.01 level) with CO/Tar and CO/puffs;F5 (named chlorine component) has positive significant correlation (at 0.01 level) with CO yield and CO/puffs. F3 and F6 had positive significant correlation (at 0.05 level) CO/puffs. In conclusion, smoldering velocity of cigarette rod, crude fiber, K and Cl have strong influences on CO yield behavior in mainstream smoke of flue-cured tobacco.