Abstract:【Objectives】Nitrogen supplying forms affect the yield of flue cured tobacco and the main chemical component contents, thus, affecting the economic quality. In this paper, the proper form of nitrogen and the ratios of different nitrogen fertilizers were studied in order to provide a theoretical basis for rational application of nitrogen. 【Methods】A field experiment with five different ratios of NH+4/NO-3 in fertilizer was conducted to study the effect of different ratios on the yield, quality of the fluecured tobacco. The changes of the main chemical components in the flue-cured tobacco caused by the ratio of NH+4/NO-3 were investigate at the same time.【Results】The application of nitrogen fertilizer with higher nitrate ratio can promote the early growth and quick tiller of flue-cured tobacco, but this effect becomes negligible at the late stages of growth. With the ratio of 50% nitrate nitrogen+50% ammonium nitrogen, the percentages of high grade tobacco are significantly increased, and the scores of mid-high grade proportion and high grade proportion reach 0.88 and 0.55. The contents of total sugar, reducing sugar, starch, potassium, fructose, sucrose and maltose are positively correlated with the ratio of NO-3 significantly. On the contrary, the contents of total nitrogen，nicotine，nitrogen-nicotine ratio，nornicotine，anabasine and anatabine show significant negative correlation with it. The lowest score of flue-cured tobacco quality is obtained with the 100% nitrate nitrogen treatment (Score 82.5), the highest score with treatment of 50% nitrate nitrogen with 50% ammonium nitrogen (Score 97.8). Therefore, when the level of nitrogen application is 150 kg/ha, the ratio of 50% ammonium to 50% nitrate will be the most suitable ratio for the tobacco-growth and quality, profit in Nanxiong area, Guangdong province.