Abstract: The changes of various fractions of phosphorus (P) separated with Tiessen-Moir method and its availability under long-term fertilization were investigated, in order to provide a theoretical basis for the reasonable application of P fertilizers in the Fluvo-aquic soil. Different fertilization treatments included no fertilization (control, CK), single application of urea (N2), no potassium (K) fertilizer (N2P); no P fertilizer (N2K), low amount of nitrogen (N) fertilizer combined with P and K fertilizers (N1PK), balanced fertilization (N2PK), medium or high amount of fertilizers (N3PK), high amount of N fertilizer combined with P and K fertilizers (N4PK), chemical combined with organic fertilizers (N2PKM), chemical fertilizers combined with corn straw returning (N2PKS). The correlation between soil P and available P and total P were analyzed. After 28 years of different fertilization treatments, the P fraction contents in the N2PKM treatment were decreased in the order of hydrochloric acid extractable P (HCl-P) > residual P (Residual-P) > sodium hydroxide extractable inorganic P (NaOH-Pi) > sodium hydroxide extractable organic P (NaOH-Po) > sodium bicarbonate extractable inorganic P (NaHCO₃-Pi) > Water-soluble P (Resin-Pi)> sodium bicarbonate extractable organic P (NaHCO₃-Po). Compared with CK, N2, and N2K treatments, N2P, N1PK, N2PK, N3PK, N4PK, N2PKM and N2PKS treatments significantly increased the contents of Resin-Pi, NaHCO₃-Pi and NaOH-Pi, while the contents of NaHCO₃-Po, NaOH- Po, HCl-P and Residual-P were not significant among different treatments. Except for NaOH-Po, the correlations among the contents of the other P fractions, available P and total P in the soil were significant. The contribution of Resin-Pi to available P was the most, indicating that Resin-Pi was the most effective source of P. The application of organic fertilizers significantly increased the contents of various P fractions in the soil, especially in the N2PKM compared with N2PK treatments. The contents of various P fractions in the N2PKS treatment were also significantly higher than those in the chemical fertilizer application treatments. The contents of soil medium and medium active P were significantly correlated with those of available P and total P in the organic fertilizer and straw treatments(N2PKS). Organic fertilizer or straw could be applied to fluvo-aquic soil to maintain a high percentage of soil available P pool.