Abstract: Phosphate immobilization and its inhibition in the soil under a Chinese fir (Cunninghamia lanceoata)stand were studied. The results showed that the immobilization of the soil is so strong that most of phosphorus was immobilized. The tree roots had the effect of inhibition on phosphate immobilization to a certain extent,Therefore, the phosphorus immobilized in rhizosphere was less than that in root zone and unroot zone. Organic acid had such effect too. Among them humic acid had the strongest effect on decreasing phosphate immobilization. The second was citric acid, and the third was tartaric acid. When the humic acid, citric acid and tartaric acid were added to soil at 2 5,5 0 and 5 0g穔g^-1 respectively, they can protect a lot of phosphorus from immobilization if the acid added to soil was more than 2 5 or 5 0 g穔g^-1, their influence would decrease gradually. So we should mix right amount of organic acid with fertiphos when they are applied in forest soil. It, therefore, was necessary to do so for rational application of fertiphos.