In order to explore the role of SPAD value in the diagnosis of nitrogen nutrients in flue-cured tobacco，using Yunyan 100 as the test material，6 field trials were set up with different nitrogen fertilizer levels，the relationship between SPAD value of flue-cured tobacco leaves，nitrogen nutrition diagnostic indicators，and nitrogen application rate were analyzed and the effect of nitrogen application rate on yield was investigated.The results showed that the yield and nitrogen application rate were related by quadratic function，which was Y=-0.07X2+18.07X+2165.34.According to the relationship between yield and nitrogen application rate，the optimal economic fertilization rate was determined to be 124.5 kg/hm²，and the corresponding optimal economic yield was 3330.4 kg/hm².The recommended fertilization standard for flue-cured tobacco based on the leaf SPAD value was established.Among them，the most suitable SPAD range was 37.11～46.06，which can be used as an index for the diagnosis of nitrogen nutrition in the resettling group tree stage and prosperous stage， and the application of nitrogen fertilizer can be recommended.