Effects of different nitrogen application rates on sweet potato yield and nitrogen use efficiency under different soil fertility conditions were explored. Field experiments were carried out to investigate the effects of nitrogen fertilizer on yield, yield components, dry matter accumulation and nitrogen use efficiency of Yanshu25, under different soil fertility levels. As results showed, without nitrogen fertilizer, the number of branches, the length of the longest stem, the leaf area index, and the yield were following this order: high soil fertility＞middle soil fertility＞low soil fertility, and the differences were significant. Nitrogen fertilizer could increase the first three indices under three soil fertility conditions (p＜0.05), but had no significant effect on the number of the largest internodes. Field plots with high, middle and low fertility levels gained the largest yields when nitrogen fertilizers were 50, 100, and 150 kg/hm2, respectively, which increased by 16.06%, 29.63% and 33.33%,respectively, compared to the control. Besides, nitrogen fertilizer could increase accumulation of above-ground dry matter s of sweet potato under all soil fertility levels. Lastly, with the increasing of nitrogen addition, the nitrogen accumulation were increased for middle and low fertility of plots, but first increased and then decreased for high fertility of plots. With the increasing nitrogen application rates, nitrogen use efficiency decreased under the high fertility, while increased under the low fertility, and was the highest under the middle fertility with 100 kg/hm2. The optimum nitrogen application rates for sweet potato in high, middle and low soil fertility are 50, 100 and 150 kg/hm2, respectively.