Sorghum [Sorghum bicolor (L.) Moench] is an important plant in an arid and semi-arid part of China. The application of nitrogen is a basic element necessary for sorghum growth. In this study, Keza15 and Suiza7 were used as experimental materials in northern china to study the relationship among nitrogen and the accumulation of starch and the yield. The results showed that the total starch accumulation of the low-N-sensitive variety had a larger change range than the low-N-tolerant varieties. From 7 to 21 days after powder dispersal was a rapid growth period of starch accumulation and played an important role in the starch synthesis of grains. The yield of the two different genotypes of sorghum increased first and then decreased with a higher rate of nitrogen application. The best nitrogen application amount was 200 kg N ha(-1) (N200). The application of nitrogen was beneficial for the increase of Soluble starch synthase (SSS), Starch branching enzyme (SBE), Bound starch synthetase (GBSS), Adenosine diphosphate glucose pyrophosphorylase (AGP), Uridine diphosphate glucose pyropitase activities (UGP), but the excessive nitrogen application led to a decrease. The effect of nitrogen on the activity of starch related enzymes for the low-N-sensitive sorghum was stronger than that for the low-N-tolerant sorghum.