Abstract: The effects of long-term fertilization on inorganic phosphorus fractions and their availability in Shajiang black soil were studied using the fraction classification developed by Gu Yi-chu and Jiang Bo-fan. The results show that nutrition efficiency of Ca2-P and Ca8-P is higher than that of Al-P and Fe-P respectively, and Ca10-P and O-P have some availability when soil phosphorus is depleted. The contribution rates of Al-P and Fe-P for plant are the highest, while those of Ca2-P and Ca8-P are low although the two fractions have high availability. To some extent, the contribution rate of Ca2-P is even lower than that of Ca10-P and O-P when soil phosphorus is extremely depleted. The accumulated phosphorus is mainly transformed into the fractions of Al-P, Fe-P, O-P and Ca10-P, while the transformation to Ca2-P and Ca8-P are little. The results of correlation and path analyses indicate that soil available P is significantly correlated to Ca2-P, Ca8-P, Fe-P, Al-P, O-P and Ca10-P. The contribution of the different inorganic phosphorus fractions to soil available P is Al-P＞Ca8-P＞Ca2-P＞Fe-P＞O-P＞Ca10-P.