Abstract: In order to clarify the characteristics of tobacco residue decomposing under waterlogged conditions and their effects on water quality, the simulated pot experiment was conducted to study the decomposing rate, decomposing amount and nitrogen, phosphorus, potassium, carbon and nicotine release characteristics of tobacco residues under waterlogged conditions, and the dynamic changes in nicotine, nitrogen, phosphorus, potassium, pH, chemical oxygen demand, and biochemical demand of water bodies after tobacco residue decomposing. The results showed that, (1) After decomposition of tobacco residues, the rate of decomposing, nutrient and nicotine release were fast at the early stage and slow at the late stage. The cumulative release rate of nicotine reached 98.6% and 99.1% respectively after 30 days. After 60 days, the cumulative release rates of nitrogen, phosphorus, potassium and carbon in tobacco stems reached 85.0%, 85.5%, 91.0% and 48.1%, and that in tobacco roots reached 71.1%, 50.8%, 87.0% and 44.4%, respectively. After 120 days, the cumulative decomposing rates of tobacco stems and tobacco roots reached 66.2% and 51.0% respectively. (2) The decomposition of tobacco residues led to rapid increase of nicotine content in water, which reached the maximum value 4 to 10 days after and the decomposition completed within 40 to 50 days. After tobacco residue being decomposed, the contents of N, P and K in water reached the maximum value from 30 to 60 days, the pH of the water reaches the maximum value from 40-50 days, the BOD₅ and COD_Cr of water reached the maximum around the 30th day of decomposition. As a result, the content of N, P, K and organic matter increased after tobacco residues decomposing and the released nicotine will decompose completely within 40 to 50 days in water; The roots and stems of tobacco met the Standards for irrigation water quality after decomposing for 40 and 60 days.