Abstract: The purpose of this study is to find the optimum amount of nitrogen of ‘Yunyan 87’ in natural conditions, which provides a certain reference for the field planting of ‘Yunyan 87’. Selected grown under natural conditions of ‘Yunyan 87’ tobacco for the test material, set 3 different nitrogen levels, 60 kg/ hm2, 82 kg/ hm2 and 105 kg/ hm2 （4 kilograms per mu, 5.5 kilograms per mu and 7kilograms per mu） to contrast, as treatment 1, treatment 2 and treatment 3. Taking four sampled three fresh leave on 7th, 10th, 13th and 15th in same leaf position before and after topping, determining stable carbon isotope (δ13C value), specific leaf weight, , total nitrogen, C/N ratio and so on. The results show that: the same climatic conditions of different nitrogen treatment environment, photosynthetic pigments and total nitrogen of treatment 3 are the highest, C/N ratio and specific leaf weigh are the lowest; specific leaf weight, δ13C value and total carbon of treatment 2 are the highest, total nitrogen and C/N ratio are slightly lower than treatment 3; δ13C value, carbon and nitrogen metabolism and other aspects of performance are poor. This study think the performance of ‘Yunyan 87’ tobacco in 82 kg/ hm2 (5.5 kilograms per mu) of nitrogen is the best, 105 kg/ hm2 (7 kilograms per mu) of nitrogen comes second, while the performance of ‘Yunyan 87’ tobacco under 60 kg/ hm2 (4 kilograms per mu) of nitrogen is poor. Accordingly, it can be determined that ‘Yunyan87’ is more suitable for planting under 82 kg/ hm2 (5.5 kilograms per mu) of nitrogen.