Abstract: The transformation and supply levels of nitrogen in tobacco-growing soil at different growth and development stage of flue-cured tobacco and its effects on the nicotine contents of upper leaves were studied.The results showed that the inorganic nitrogen content in soil layer depth of 0-20cm raised sharply but only for a short time by inorganic nitrogen fertilizer application;the inorganic nitrogen content in the layer depth of 20-40cm was affected slightly by nitrogen application;oversupply of nitrogen at latter growing stage led to excessive nicotine content in upper leaves.