【Objective】This research aims to investigate the characteristics of phosphorus forms in soil aggregates, iron oxids and the distribution of phosphate-solubilising bacteria in different forest types, and to reveal the relationship between phosphorus forms and forest type transition, so as to provide a reference for the understanding of the influence mechanism of soil phosphorus cycling in vegetation restoration and the assessment of soil quality.【Method】Soil samples were collected from fixed plots of bare land (BL), coniferous forest (CF), mixed coniferous broad-leaved forest (MF), and broad-leaved forest (BF) at the National Positioned Observatory for Red Soil Hills Ecosystems in Changting County, Fujian Province, China, and analysed the composition of soil agglomerates of all grain sizes by the dry sieve method, and the phosphorus content [total phosphorus (TP), effective phosphorus (AP), inorganic graded phosphorus, and the content of iron oxides (Fe_d), amorphous iron (Fe_o), and complex iron (Fe_p)] of aggregates of all grain sizes, respectively, were measured by the dry sieve method, and combined with the high-throughout sequencing for the determination of the characteristics of phosphorus-solbuiling bacterial (PSB) community structure and composition.【Result】(1)Soil aggregates were classified by particle size into <0.25 mm (micro-aggregates), [0.25, 2.00] mm (small aggregates), and >2.00 mm (large aggregates). The proportions from low to high were: micro-aggregates, large aggregates, and small aggregates. small aggregates were dominant, with a proportion ranging from 40% to 53%.(2) During the transition of forest types, the inorganic phosphorus content in soil aggregates primarily existed as occluded phosphorus (O-P), which accounted for over half of the total inorganic phosphorus. Calcium phosphorus (Ca-P) displayed an initial increase followed by a decrease. Moreover, the content of aluminum phosphorus (Al-P) and iron phosphorus (Fe-P) rose with the decrease in particle size of soil aggregates. (3) Within the same particle size of soil aggregates, free iron oxide (Fe_d) contents generally decreased, while complexed iron oxide (Fe_p) contents generally increased. The content of amorphous iron oxide (Fe_o) in >2.00 mm aggregates generally increased, and in [0.25,2.00] mm and <0.25 mm aggregates, it first increased, then decreased, and increased again. (4) A reduction in soil aggregate particle size was associated with an overall increase in the richness of PSB (Chao1, observed_species) and a general decrease in PSB diversity (Shannon, Simpson) with the transformation of forest types. 【Conclusion】As vegetation transitions from bare land to broad-leaved forests, the concentrations of amorphous iron oxides and complex iron forms increase, facilitating the formation and maintance of larger soil aggregates. However, PSB preferentially inhabit microaggregates and small aggregates, highlighting the critical role that these smaller aggregates play in supplying effective phosphorus within mature forest ecosystems.