In order to improve the applicability of multi-spectral image nitrogen nutrition diagnosis，six field trials with different nitrogen levels were set up with flue-cured tobacco as the research object，the multispectral image of flue-cured tobacco growth was regulary taken to test the nitrogen content of the plant.The correlation between vegetation index (NDVI，GNDVI，LCI，NDRE，OSAVI) and traditional nitrogen indicators，and the response between the optimal vegetation index and nitrogen application rate were analyzed.The results showed that the optimal monitoring period for flue-cured tobacco was around 50 days after transplanting，each vegetation index was most sensitive to the nitrogen content of single plant.The judgment standard of using vegetation index guiding the top dressing of field fertilization was Nnow=1911NDVI-1345.1，which provided new ideas and key technologies for high-quality top dressing of crops in a large area.