Abstract: Under medium-cultured condition of bagasse, the rubber tree root was treated with 0,20,40,80…5120 mg/kg N, to investigate responses of root growth at different nitrogen supplying levels. Results indicated that the tested root traits group (including the number of roots, dry weight of roots and total length of roots) responded positively to nitrogen concentration, but the increment declined as nitrogen concentration increased. But the base traits group (including length, diameter per unit of the root) showed negative response to nitrogen concentration respectively. These effects indicated that nitrogen has an important modulation function to the roots.