Abstract: Maize(Zea mays L.) was grown in quartz sand culture either with a normal root system (co- ntrols) or with seminal roots and primary root(treatmentⅠ, ‘double-rooted’),with primary root only (trea- tment Ⅱ, ‘single-rooted’).Development of adventitious roots was prevented by using plants with an eti- olated mesocotyl and the stem base was positioned 5 cm -8 cm above the sand(Fig.1Da). As compare with controls, the growth of the whole plants(Table1) and their shoots(Fig.1A), their ratio of absorption root to shoot (Fig.3)were restricted as roots were restricted. Even though the net increments in dry we- ight(Table6), N contents(Table6) and N contents(Table5) of whole plants which had either with seminal roots and primary root or with primary root only were obviously decreased during a 10-d study period, but they enable the plants to restore the more strongly N use efficiency by some compensatory growth mechanisms under root system was restricted, such as increments in N allocation of shoots was obvio- usly increased(Table5),the N absorption efficiency of roots was greatly increased(Fig.2). As compare with controls, among the root characteristics of treatmentⅠand treatment Ⅱthat were analyzed, root length had strongest effect on the root function, root dry weight had the weakest effect, root surface area and root volume which had similar effect on the root function was intermediate. Between treatment Ⅱ and treatmentⅠ, root dry weight had strongest effect on the root function, root volume had the weakest effect, root length and root surface area which had similar effect on the root function was intermediate. The results indicated that root length was more important to the root function than the root dry weight when there was great difference in different plant root volume, but root dry weight was more important to the root function than the root length when different plant root volume was similar.