A field experiment was conducted to study the effects of different application rates of nitrogen fertilizer on yield, mineral nutrient uptake, nitrogen use efficiency, agronomic efficiency and economic benefit under two soil fertility conditions. The results showed that all of biomass, yield, increased yield, nutrient uptake, nitrogen use efficiency and agronomic efficiency for Sushu No.8 were greater in the high fertility soil compared with the low one. In the two fertility soils, the fresh weight of stems and leaves increased with the increase of nitrogen application, the fresh weight of root and the vine-tuber ratio increased firstly and then dropped with the increase of nitrogen application. With the increase of nitrogen application, nitrogen use efficiency, yield and increasing unit of Sushu No.8 firstly increased and then dropped, but nitrogen agronomic efficiency gradually reduced. In the condition of low fertility soil, a total of 5.46 kg of nitrogen, phosphorus and potassium fertilizers was needed to produce every 100 kg dry tubers of sweet potato, with a ratio of N︰P2O5︰K2O=1.00︰0.32︰1.03, however, in the high fertility soil, a total of 7.09 kg of nitrogen, phosphorus and potassium fertilizers was needed with a ratio of N︰P2O5︰K2O=1.00︰0.43︰1.39. Considering the yield, nitrogen use efficiency and economic benefits, we recommended that N 95-110 kg/hm2 and 110 -120 kg/hm2 should be applied for the low and high fertility soils, respectively.