Abstract: A study was made on the distribution characteristics and biomass of individual tree root system as well as root distribution characteristics of stands in different densities of the narrow-crown clone of black locust(Robinia pseudoacacia cl.Zhaiguan),by using the methods of digging out whole root system of the individual and digging out root pieces in different vertical and horizontal locations in the soil of the stands.The result showed that the root distribution between the individual trees and tree lines extended horizontally to 6.6 m and 5 m respectively;and the taproot vertically extended to 2 m below the ground surface with its lateral roots mainly distributing in the soil from 10 cm to 40 cm below the ground surface.The biomass of whole root system accounted for 16.82% of the biomass of whole individual tree,with the biomass of taproot and lateral root taking about 87.13% and 12.87% of the biomass of whole root system.The total biomass and length of the roots of Zhaiguan clonal stands were 6 160.2-10 940.55 kg·hm-2 and 970.35-1 607.4 km·hm-2 respectively,and showed a positive relation with the stand densities.In vertically,the roots with diameter less than 15 mm mainly distributed in the soil from 0 to 20 cm below the ground surface,while the roots with diameter more than 15 mm mainly distributed in the soil from 20 to 40 cm below the ground surface.In horizontally,the biomass and length of the roots with diameter equal to or more than 5 mm decreased while the biomass and length of the roots with diameter less than 1 mm increase with the increasing of distance from tree stem in the stand.The roots with diameter less than 1 mm mainly distributed horizontally from 0.5 m to 1.5 m away from the tree stem in the soil of the stand.