Under conditions of different nitrogen application rates, the leaf area index, photosynthetic potential, dry matter accumulation, yield components and economic benefits of sweet potato were studied in different growth stages. The results of two years of test in 2017 and 2018 showed that when the nitrogen application rate was 210 kg/ha,the leaf area index, photosynthetic potential, storage root dry matter accumulation were increased in different growth stages, which promoted more and heavier fruits, yield was increased significantly. But when the nitrogen application rate was as high as 300 kg/ha, the storage root yield was reduced. When nitrogen application rate was 210 kg/ha, the two years yields of sweet potato all reached maximum of 41 034.55 kg/ha and 42 131.25 kg/ha, respectively.