During the last decades, long-term fertilization has improved soil fertility in the Huang-Huai-Hai Plain. With increasing soil available P, crop response in yield to phosphorus fertilization has been found declining, while environmental risks of unreasonable fertilization are becoming an hot issue of concern. In recent years, returning straw to fields is a farming practice getting more and more popular in the Huang-Huai-Hai Plain, however, few studies, let alone long-term straw return field experiments, have been carried out to investigate impacts of such changes in field management on fractions of soil inorganic P, soil P availability, yield response as well as potential environmental risks. Therefore, based on the 33-year long-term fertilization field experiment effects of straw return in conjunction with chemical P fertilization on total-P, Olsen-P as well as fractions of inorganic phosphorus in fluvo-aquic soil in the Huang-Huai-Hai Plain were studied. Fractionation of inorganic P was done using the Gu Y-C, Jiang B-F method. In this experiment, the split-plot method was used, and 4 main plots, i.e. N₀S₀, N₁S₁, N₂S₂ and N₃S₃ were laid out. Each main plot was split into 3 sub-plots, applied with straw at a rate of 0, 2250 and 4500 kg hm^-2, separately. This experiment under a winter wheat-summer maize rotation system was initiated in 1981, and designed to have maize straw returned to the field in 1981-1983, 1987-1989, 1993-1995, 1999-2001 and 2005-2013 and winter wheat straw returned in 2000 and on. Results show that among the plots the same in P₂O₅ application rate, (0, 60 or 20 kg hm^-2 in chemical phosphorus), those having maize straw returned for 21 years and those having wheat straw returned for 15 years witnessed soil Ca₈-P significantly increased with rising straw return rate; in plots applied with P₂O₅ at 240 kg hm^-2 in chemical phosphorus, soil total P, available P and inorganic P, such as Ca₂-P, Ca₈-P and Al-P, were all significantly increased with rising straw return rate, but Fe-P, O-P and Ca10-P did not change much in content. Compared to Plot N₀P₀S₀, Plot N₀P₀S₂ (maize straw returned at 4500 kg hm^-2) was 10.2% or 7.33 mg kg^-1 higher in content of soil Ca₈-P; compared to Plot N₁P₁S₀, Plot N₁P₁S₂ was 32.5% or 24.39 mg kg^-1 higher in content of soil Ca₈-P; compared to Plot N₂P₂S₀, Plot N₂P₂S₁ was 10.3% or 10.07 mg kg^-1 and Plot N₂P₂S₂ was 27.3% or 26.71 mg kg^-1 higher in content of soil Ca₈-P; and in comparison with Plot N₃P₃S₀, Plot N₃P₃S₁ and N₃P₃S₂ was 64.5% or 2.47 mg kg^-1and 178.6% or 6.84 mg kg^-1 higher in content of soil Ca₂-P, 42.0% or 80.15 mg kg^-1 and 67.8% or 129.3 mg kg^-1 higher in content of soil Ca₈-P and 37.0% or 15.68 mg kg^-1 and 61.7% or 26.14 mg kg^-1,higher in content of Al-P, respectively. In terms of relative increment (p<0.05) the fractions of inorganic P displayed an order of Ca₂-P＞Ca₈-P＞Al-P. In addition, in the plots the same in straw return rate, impacts of chemical P fertilization rate on soil P were also examined: in comparison with Plot N₀P₀S₀, Plots N₁P₁S₀, N₂P₂S₀ and N₃P₃S₀ had soil total P, inorganic P and Olsen-P increased on average by 154, 164 and 7.24 mg kg^-1(23.1%, 35.9%, 593.2%), respectively, and Ca₂-P, Ca₈-P, Al-P and Fe-P increased on average by 1.53, 49.43, 14.18 and 13.09 mg kg^-1 (242.9%, 68.9%, 59.5% and 40.7%), respectively. Furthermore, in comparison with N₀P₀S₀, Plots N₁P₁S₁, N₁P₁S₂, N₂P₂S₁, N₂P₂S₂, N₃P₃S₁ and N₃P₃S₂ had soil total P, inorganic P and Olsen-P increased on average by 2013, 271 and 9.90 mg kg^-1 (35.1%, 59.1%, 811.7%), and Ca₂-P, Ca₈-P, Al-P and Fe-P increased by 3.67, 97.65, 22.99 and 17.04 mg kg^-1 (581.7%, 136.1%, 96.6% and 53.0%), respectively. In conclusion, in the farmlands under the winter wheat-summer maize rotation system in the Huang-Huai-Hai Plain, when P input falls lower than P output (120 kg hm^-2), the soils would not have much changes in total P, inorganic P, Olsen-P and fractions of inorganic P, regardless of whether straw is returned in addition to fertilization. However, when P input goes beyond P output, soil total P, Olsen-P as well as Ca₂-P, Ca₈-P, Al-P and Fe-P will all increase, and among the P fractions, Olsen-P ranks first in relative increment, and is followed by Ca₂-P, Ca₈-P and Al-P. In addition, balance of soil phosphorus input and output is positively related to contents of the various fractions of soil phosphorus (p<0.05).