Abstract: Competitive adsorption of phosphate and organic acid ligand on Al (OH)x surface was studied under various concentration ratio of phosphate to oxalate (Cp/Cox) or addition order, mixture of several organic acids, and equilibrium time The results showed: (1) The effect of organic acid on decreasing phosphate adsorption varied with the addition order of them When the organic acid was introduced before phosphate addition, the effect of organic acid on P adsorption was the most remarkable; but when the organic acid was added after phosphate addition, it was the least effective; and when they were added as a mixture or when phosphate was added after organic acid was sorbed, then discarded through centrifuging, the effect of organic acid was in the middle (2) When phosphate was added as a mixture with two or three kinds of organic acids to Al (OH)x mineral, the reduction of phosphate adsorption amount by Al (OH)x was different with that in the system of single organic acid The reduction degree was related to the kind and concentration of organic acids Because of the competition among phosphate and different organic anions, the final effect was not equal to the sum of single organic acids (3)The amount of phosphate adsorption in the presence of citrate or oxalate was increased with the equilibrium time prolonging from 1 to 7 days The relative affinity played a more important role for competitive adsorption