Abstract: The experiment was conducted to study the activity of root system and the regulation of nicotine accumulation at different topping time on cinnamon soil in Xuchang, Henan Province in 2005. The activity of root system was significantly positively related to nicotine level. As the topping time delayed, the activity of root system and nicotine level increased slowly and declined rapidly from the peak value. The topping time was significantly negatively related to nicotine level in middle and upper leaves. The highest nicotine level in middle leaves appeared with topping on early button period and the highest rate of nicotine accumulation occurred about 20 days after topping. The highest rate of nicotine accumulation in upper leaves occurred 80 days after transplanting，and declined gradually with topping stage delayed. Nicotine level also declined gradually, 0.0504 percent with delaying one day.