Abstract: It is well known that excessive N application brought about severe environmental pollution in developed(regions),in the meanwhile,N application was insufficient and resulted in low yield in undeveloped regions.Developing N efficient plant was a good way to solve this problem.There were many studies on N efficiency of plants,but few studies were focused on the genetics of roots especially the lateral roots,which related to N uptake.It was helpful to study the inheritance of root traits especially on lateral roots and axial roots under nitrogen stress to understand the heterosis of(hybrid) on N uptake.In this study, the general combining ability(GCA),special combining ability(SCA) and the (genetic) ability for each root trait were analyzed under both high and low N levels using 7 inbred lines,with NCⅡ design(43).In greenhouse,the experiment was conducted with 7 maize inbred lines and their crosses and sand-culture (under) two N levels(4 and 0.04 mmol N/L).The genotypic variations of GCA and SCA on root traits among different genotypes were observed at HN and LN(table 2,3). The GCA between length of lateral root and the total length of axial roots contributed to the root length under both N levels,but first one played a dominant role.So did the SCA of root traits at HN and LN.At HN,all root trait parameters of the SCA variance was higher than that of GCA of root traits except numbers of axial roots,while the root trait parameters of SCA variance was lower than that of GCA except the length of axial roots(table 4).The H(B) of root dry weight,root length and length of lateral root were higher at both two N levels.At LN,H(B) of all root trait parameters decreased while H(N) of root dry weight,root length and length of lateral root(increased)(table 4).In conclusion,the root inheritance traits of maize was influenced significantly by N stress.There are significant genotypic differences on the responses of the GCA and SCA of root traits to N stress.The genetic of root traits were controlled by non-additive effect at HN,but by additive effect at LN.