Split–plot design was used to investigate the influence of nitrogen rates(low–nitrogen about 195 kg/hm2, medium–nitrogen about 225 kg/hm2, high–nitrogen about 255 kg/hm2), numbers of remained leaves(14, or 16, or 28, or 20 leaves each tobacco) and their interaction on the chemical constituents and TSNAs of sun–cured red tobacco Wanmao No.3. Results showed that compared to low–nitrogen treatment, the total nitrogen content in medium–nitrogen and high–nitrogen treatment was increased by 6.1% and 16.5%, respectively, the nicotine content was increased by 13.3% and 39.0%, respectively, the K+ content was increased by 6.2% and 12.9%, respectively, the nitrate content was increased by 9.3% and 19.7%, respectively and the total sugar content was increased by 16.1% and 29.9%, respectively. Compared to treatment with 14 leaves remained, the total sugar content in treatments with 16, 18 and 20 leaves remained was increased by 9.4%, 28.4% and 31.6%, respectively, the K+ content was increased by 10.2%, 12.8% and 20.6%, respectively, the total nitrogen content was decreased by 4.5%, 9.5% and 12.4%, respectively, the nicotine content was decreased by 7.1%, 18.2% and 21.9%, respectively. Increase in nitrogen rates or reduction in numbers of leaves both resulted in significant increase of TSNAs content. Interaction between nitrogen rates and numbers of leaves has a great influence on chemical constituents and TSNAs content. The nitrogen rates had more significant impact on the nicotine, K, TSNAs, total alkaloid and nitrate content while the numbers of leaves had more significant impact on the sugar content and nitrogen–nicotine ratio. Comprehensive analysis by fuzzy indicated that tobacco leave’s chemical components are coordinate under nitrogen rates 225 kg/hm2 and 16 leaves per tobacco plant.