In order to demonstrate the mechanism of nitrogen stress and different nitrogen forms on glucose metabolism of tobacco seedlings,we used ‘Zhongyan 100’ as the material.Sand culture were adopted in the normal supply of nitrogen (CK,NO₃^-∶NH₄⁺=1∶1),nitrogen deficiency (T₁),single ammonium (T₂) and single nitrate (T₃) of the four treatments.The contents of reducing sugar,total sugars,sucrose,starch and the activities of glucose metabolism-related enzymes in functional leaves of tobacco plants were detected.Meanwhile,we analyzed the differences of key glucose metabolism genes (SUT1,INV,GBSSI,AGPase) in roots,stems,leaves.The results showed that:(1)The total N in four treatments are T₃>CK>T₂>T₁.(2)The contents of sugar,total sugar,sucrose and starch in tobacco leaves of T₁ were increased significantly (P<0.05) compared with CK during early plant development;The amylase activity was significantly reduced,however the invertase activity was different (P>0.05).The accumulation of starch in four treatments are T₁>T₂>CK>T₃.（3）The glucose metabolism gene expression showed that SUT1,INV,AGPase,GBSSI were expressed significantly in T₁,T₂ and T₃,indicating that biosynthesis of grain starch in T₁,T₂ and T₃ were more active.Altogether,our data suggest that the accumulation of starch and nitrogen utilization rate are inversely proportional,and the SUT1 gene may be very important in starch biosynthesis under different nitrogen forms.