A field experiment was conducted to investigate the roots characteristics and the correlations between the aboveground and underground parts of 20 Populus clones. The results showed that their root systems are mainly concentrated in 0～50cm soil layer, the root system is given priority to with horizontal root, vertical root basic disappearance, adventitious roots of small Angle, with the ground close to the level.Zhongzhu 1, NL 351, T 26 and zhongzhu 6 had larger total length of adventitious roots and zhongzhu 1, zhongzhu 6, NL 351 and I 107 adventitious roots in the total quantity is more which the ground diameter under 2cm accounted for 60％～80％ of total number of adventitious roots. The growth indexes between the aerial and underground parts, exists significant correlation relationship, such as height, crown diameter, root weight and root length. The root／shoot ratio ranged from 0.23 to 0.45. The root length per unit shoot weight differences is bigger, the biggest for T26, the smallest for zhonghe 1. The root absorption efficiency was significantly negative correlated with the root／shoot ratio and the root length per unit shoot weigh, known as root redundancy. By cluster analysis, 20 Populus clones were divided into 3 groups and 6 categories at similarity coefficient 1.3. The results may provide a theoretical basis for further breeding improved clones of poplar and management.