Abstract: This study used pot experiments to investigate the cadmium (Cd) uptake potential of alfalfa (Medicago sativa) and to explore the possible mechanisms involved in root adaptation under various levels of cadmium stress (0, 10, 25, 50 mg/kg). Alfalfa shoot biomass, root biomass, total root length, root surface-area, root volume, average root diameter and root number were all significantly smaller under the three Cd stress treatments than in the normal Cd condition (P<0.05). Shoot biomass was 87.8%, 56.5% and 14.3%, and root biomass was 96.1%, 63.3% and 16.2% respectively. The highest Cd content was observed in fine roots (root diameter below 1.0 mm) and the Cd content in shoots was higher than that in roots with diameters above 1.0 mm. The Cd content in three parts (shoot, fine root, coarse root) increased significantly with increasing Cd exposure. The highest Cd accumulation was recorded in shoots (7.715 μg/plant) at a concentration of 25 mg/kg Cd. Compared to the control, root length, root surface-area and the root volume of different diameter classes decreased significantly with increases in Cd concentration, except for the proportion of roots with diameters below 0.5 mm, which increased. It can be concluded that alfalfa is suitable for remediation of Cd polluted soil when Cd concentrations are less than 25 mg/kg and the response characteristics of root systems to Cd show dynamic equilibrium.