Abstract: 【Objectives】Reasonable nitrogen supply greatly boosts crop yield and quality. The optimum amount of nitrogen was determined to investigate the effect of nitrogen fertilizer on yield formation of storage root, nutritional quality and starch pasting properties. 【Methods】 A field experiment was carried out using two sweet potato cultivars, Xushu 28 and Xushu 22. Five N application rates were designed: 0, 60, 120, 180 and 240 kg/hm2, respectively. The sweet potato leaf area index, photosynthetic potential, dry matter accumulation index and yield components were investigated in different growth stages. The nutrient quality indicators of storage root were determined using spectrophotometric method. Tech-master type RVA was used for the rapidly determination of the viscosity characteristics of starch. 【Results】 The leaf area of sweet potato, the photosynthetic potential, and storage root yield were increased by the N application, the highest yield increase of 16.38% for Xushu 28 and 9.31% for Xushu 22 were obtained under the treatment of N 60 kg/hm2, but when the N rate was as high as 240 kg/hm2, the storage root yield was reduced. N rate would not remarkably reduce the content of the starch and amylose, but increase the content of soluble sugar and sucrose significantly. Nitrogen application significantly increased the peak viscosity, hot paste viscosity, cool paste viscosity and setback values. Correlation analysis indicated that amylose content was negatively correlated with peak viscosity (r=-0.90**) and breakdown value (r=-0.71*). Amylose content was positively correlated with setback value (r=0.73*). 【Conclusions】 Comprehensive considering the yield and quality of sweet potato, N application rate of 60 kg/hm2 is a reasonable selection.