Abstract: The results of the studies on the relationship between chemical components in tobacco leaves and toxic components in the smoke were stated.It was indicated that the toxic components in the smoke were closely related to the chemical components in tobacco leaves.Majority of the toxic components in the smoke were produced through the decomposition of the chemical components in the leaves under high temperature during smoking, while some of them were produced through the transportation of the same toxic components of the leaves into the smoke.Different kinds of chemical components in the leaves produced different kinds of toxic components through smoking.