Abstract: For analyzing the relationships between chemical components and sensory quality of tobacco leaves, an identification method for nonlinear relationship was developed based on generalized additive models. The linear and nonlinear relationships between four routine chemical components (total nitrogen, nicotine, total sugar and reducing sugar) and sensory evaluation indexes of 497 samples of middle leaves of flue-cured tobacco from main tobacco producing areas in China were studied. The results showed that: 1) At the significant level of 0.05, total nitrogen significantly negatively linearly correlated to aroma quality and quantity, offensive odor, irritancy and aftertaste; nicotine possessed a significantly negatively linear correlation with aftertaste and a significantly positively linear correlation with aroma quantity; total sugar and reducing sugar significantly positively linearly correlated to aroma quality and quantity, offensive odor, irritancy and aftertaste. 2) There were significantly nonlinear relationships between total nitrogen and aroma quality, offensive odor, irritancy, aftertaste; and between nicotine, total sugar, reducing sugar and aroma quality, aroma quantity, offensive odor, irritancy, aftertaste; all of them presented an obvious "∩"-shaped curve relationship; while the nonlinear relationship between total nitrogen and aroma quantity was not significant at the significant level of 0.05. 3) The appropriate ranges for total nitrogen, nicotine, total sugar and reducing sugar contents in flue-cured tobacco leaves were 1.5%-2.8%, 2.0%-3.5%, 15%-28%, and 15%-25%, respectively.