The effects of organic acids on organic phosphorus fraction in calcareous soil were studied by pot experiments. The results indicated that: the middle-labile organic phosphorus was dominant in the organic phosphorus fraction in calcareous soil, followed by the high-stable organic phosphorus and the middle-stable organic phosphorus, while the labile organic phosphorus was the lowest; the application of phosphate fertilizers (potassium dihydrogen phosphate and fluoraoatite) caused the changes of organic phosphorus content and its fraction in the tested soil; the content of organic phosphorus increased after organic acids were applied to the tested soil, which mainly attributed to the increases of the middle-labile organic phosphorus and the labile organic phosphorus, but the contents of the middle-stable organic phosphorus and the high-stable organic phosphorus decreased; organic acids promoted the activity or the bioavailability of soil organic phosphorus, thus accelerated organic phosphorus to be mineralized to inorganic phosphorus or directly absorbed by plant root system. The effect of oxalic acid in this aspect was generally stronger than that of humic acid. Under phosphorus stress, organic acids increased the phosphorus availability in calcareous soil and prompt the crop growth.