Pot experiments of alfalfa were conducted to study the effects of EDTA and CA on distribution of Ni, physiological indexes of alfalfa and changes of soil enzyme activities. The results showed that when the EDTA/CA content was 5.0/2.5 mmol·kg^-1, the Ni in the soil was better hydrated with the solubility was 48.2 times higher than that of the control group, and the content of malondialdehyde (MDA) in alfalfa increased by 232.0% compared the control group. When the concentration of EDTA / CA was 2.5/5.0 mmol·kg^-1, the transfer coefficient of alfalfa was the highest, which was 194.3% of the control group. The cell permeability of alfalfa increased with the increase of the total amount of chelating agent with the highest cell permeability observed in the group of EDTA/CA 5.0/10.0 (P <0.05), which was 206.3% higher than that of the control group. The effect of EDTA/CA on soil catalase was inhibitory in different extent and the invertase was significantly correlated with CA (P <0.01). It is suggested that the addition of EDTA/CA in an appropriate proportion can reduce the dosage of chelating agent and improve the enrichment of heavy metal Ni in alfalfa.