To investigate the effects of straw incorporation combined with different water management practices on phosphorus availability in paddy soils, and to elucidate the correlations between transformation of soil available phosphorus forms and soluble organic carbon content and Fe³⁺/Fe²⁺ ratio in soil, an indoor simulated cultivation experiment is conducted. Six treatments are designed: flooding (W1), drought (W2), alternate wetting and drying (W3), flooding + straw incorporation (W1+S), drought+straw incorporation (W2+S), and alternate wetting and drying+straw incorporation (W3+S). Changes in soil available phosphorus forms, content, and fractions are analyzed during different stages of straw decomposition. The results show that straw incorporation significantly increases soil available phosphorus content, with W1+S showing the highest levels, while W2 and W3 exhibited lower values. Flooding can fully release soluble organic carbon in soil after adding straw, with W1+S achieving the highest soluble organic carbon content and W2 the lowest. A highly significant positive correlation is observed between soluble organic carbon content and available phosphorus content. Under flooding with straw incorporation, the Fe³⁺ from Fe-P in soil is reduced to Fe²⁺, accompanied by H⁺ release, leading to a 0.48 pH decrease compared to W1, and promotes the transformation of Ca₁₀-P into more Ca₂-P and Ca₈-P in soil, significantly increasing their proportions while reducing Fe-P. Straw incorporation under flooding conditions effectively enhances phosphorus availability in paddy soils.