Abstract: The effect of organic acids on the transformation of phosphorus in calcic fluvo-aquic soil was studied under(indoor) incubation and pot culture condition.The results were following: 1) phosphorus element in form of phosphate(Ca10P,etc.) with very low availability was dominated,whereas higher availability phosphate(Ca8-P,etc.) was less and Ca2P was the least;2) Apply phosphate with different sources increased total amount inorganic phosphorus.KH2PO4 and DCP transform mainly occurred oriented to Ca8-P and Al-P etc with lower availability.OCP,FA,Fe-P and Al-P mainly exist in their own forms within a short period. 3) Organic acids addition caused the content of Ca10P,Fe-P and Al-P reduction, while caused Ca2-P,Ca8-P and O-P enhancement to a varying extent in the soil.The general tendency observed was that organic acid application promoted the transformation of phosphates in the form of less or unavailability to higher availability.These promoting ability was varying with the varieties and properties of organic acids,among which Oxalic acid Citric acid Tartaric acid.