Based on a long-term (33 years) fertilization experiment, changes in form and content of phosphorus in mountain red soil were investigated. Results show that the long-term P fertilization increased both Total P and readily available P in content in the soil, leading to significant accumulation of inorganic and organic P in the surface soil layer. In soils under P treatment inorganic fraction of P was composed mainly of Fe-P, which accounted for about 50%. Correlation analysis shows that readily available P was significantly related to Fe-P and Al-P with correlation coefficient being 0.908** and 0.706*, respectively, which means that Fe-P and Al-P are the sources of readily available P in the soil. The results also show that Fe-P increased with phosphate fertilization, but Al-P reduced, which somewhat affected the content of soil available P. Soil organic P in the mountain red soil under long-term fertilization can sorted into four forms, that is, active organic P, moderately active organic P, moderately stable organic P and highly stable organic P. Soil organic P decreased somewhat in the soils without P fertilization and increased in the soils with P fertilization. In the soils with P fertilization the four soil organic P followed a decreasing order of moderately stable organic P > moderately active organic P > highly stable organic P > active organic P, of which the first two accounted for 90% or so. Correlation analysis of organic fractions of P and readily available P shows that readily available P was significantly and positively related to moderately active organic P and moderately stable organic P, with correlation coefficient being 0.861** and 0.840*, respectively, which demonstrates that moderately active organic P and moderately stable organic P are the major sources of readily available P in the soil. It was also found that a higher application rate of P coupled with N, K and barnyard manure can promote transformation of other forms of organic P into moderately active organic P and moderately stable organic P that are easily absorbed by crops.