The experiment was carried out to investigate the interactive effects of nitrogen and potassium on the growth and development，yield formation and dry matter distribution of sweet potato，in order to provide theoretical basis for safe and efficient fertilization on sweet potato. Sweet potato cultivar“Taishu No.14”was used as tested crop，different ratios of nitrogen to potassium fertilizer were set up，and the interactive effects of nitrogen and potassium on the stem and leaves growth，yield and yield formation and dry matter accumulation and distribution were studied. The results showed that:The treatment with nitrogen and potassium application rates of 9，18 g/m2(N1K1) increased the tuber number and single tuber weight，improved increasing velocity，and increased storage root yield. The storage root yield，increasing velocity，marketable ratio of storage root and lump weight of the treatment K1 were higher than those of the only N fertilizer treatment. The storage root yield，tuber number and single tuber weight of N1K1 were the highest. The interactive effects of nitrogen and potassium could control over-growing of the stem and leaves，and reduced T/R value，increased the dry matter distribution to storage root，and the effects of the N1K1 treatment were the best remarkable. In the experiment N1K1 was the best ratio of nitrogen potassium fertilizer，which could promote coordinate growth between overground part and underground part，promote storage root expanding quickly，and increase storage root yield.