In order to reduce the tar and nicotine content of cigarette, the conventional chemical composition and the flue gas composition of the expanded leaves under different process conditions were analyzed. The result showed that: under the test conditions, the process gas temperature was higher, the contents of tar, nicotine and CO in the flue gas composition of the expanded leaves were lower when the saturated vapor was added to a certain amount; the amount of tar, nicotine and CO were the lowest when the steam was added to 600 kg/h. under the same conditions of the process gas temperature.