Abstract: To explore the effects of citric acid concentration on the remediation of uranium contaminated soil by Lolium perenne and it’s physiological characteristics，pot experiments were conducted to investigate the effects of different citric acid concentrations (0, 1, 5, 10 mmol/kg) on the growth, physiology and uranium accumulation and distribution of Lolium perenne under the environment of 15 mg/kg uranium stress. The results show that with the increase of citric acid concentrations, cell inclusion parameters including growth, photosynthetic pigments, soluble protein content, root vitality, and the activities of glutathione and several enzymes, in Lolium perenne firstly increase and then decrease. The membranous permeability, malondialdehyde contents and oxidised glutathione contents gradually increase. The uranium contents in various Lolium perenne positions firstly increase and then decrease, but the uranium contents in the root are much higher than those in the above-ground parts. The subcellular uranium distributions in cells show that the enrichment of uranium is cell wall and residue part>soluble part>organelles and membrane parts, and the enrichment of uranium firstly increases and then decreases under the same concentration of uranium. The electron microscopy images show that the environment of uranium stress can lead to irreversible damage on Lolium perenne ultrastructures, while the addition of 5 mmol/kg citric acid can reduce the damage degree. It is concluded that citric acid with low concentrations of 1 and 5 mmol/kg can promote the growth and remediation efficiency of Lolium perenne in uranium contaminated soil. And 5 mmol/kg citric acid can reach the best effect, while 10 mmol/kg can limit the growth of Lolium perenne.