Four maize inbred lines were used to compare the difference of root morphology and N uptake using different N levels and light intensity in culture solution .The results showed as follows: More proportion of carbohydrate could allocate to root by increasing light intensity. Root length , root volume and root dry weight had significantly increased compared to low light intensity for the four genotypes. The variety of Baici with low N efficiency had a decreased root biomass compared to other genotypes under N stress condition in the two light intensity. Compared to 478 with a high N efficiency, root volume and root dry weight were decreased by 27.54% and 21.24% respectively for Baici under the condition of 0.4 mmol/L and high light intensity. Therefore, decreased the amount of root N uptake for Baici . It was indicated that there had a positive interaction between N levels and light intensity on allocation of carbohydrate.