Abstract 【Objective】Phosphorus is an essential nutrient element that affects crop growth, yield enhancement and quality improvement. Due to the application of a large amount of phosphate fertilizer and the lack of scientific management, the utilization rate of phosphate fertilizer is low and the environmental risk increases. Thus, it is important to know the effects of different amounts of exogenous phosphorus (P) addition on P bioavailability components in paddy soil under flooding conditions.【 Method】Three soil samples were collected from the new paddy field (NP, 2-3 years), medium-term paddy field (MP, 20-30 years) and old paddy field (OP, 400-500 years) in Sunjia small watershed of Yingtan, Jiangxi Province. Based on the flooding culture experiment (0-80 days) with different concentrations of exogenous P addition [0 (CK), 125 (P1), 250 (P2), 500 (P3), 625 (P4), 750 (P5) mg·kg-1], the test for simulating the bioactivation process of biologically based P (BBP method) was adopted. The dynamic changes in the increment (?) of soluble P (Ca-P), easily activated and released P (Ci-P), easily mineralizable acid phosphatase (En-P), and the potential inorganic P (HC-P) were analyzed, and the correlation between all P components and influencing factors were evaluated.【 Result】The results showed that under flooding conditions, exogenous P addition could significantly increase the available P (Bray-P) and BBP components such as Ca-P, En-P, Ci-P and HC-P in paddy soil, and the increment of P contents of each component increased significantly with an extension of P addition. The increment of BBP components was changed by the order: ?Ca-P < ?En-P < ?Ci-P < ?HC-P. On day 15 of incubation, the ?Ca-P and ?Ci-P in the new paddy field reached a maximum value while on day 60, the ?Ca-P, ?En-P, ?HC-P and ?Bray-P in the medium-term paddy field reached their maximum value. However, the P content of each component did not change significantly in the old paddy field. The ratio of ΔBray-P to ΔTP (ΔBray-P/ΔTP) in paddy soil after exogenous P addition showed the same trend as that of ΔBray-P, but there was no significant difference among different P additions. Path analysis showed that exogenous P addition had a significant direct positive effect on ?Bray-P in new and old paddy soil; ?Ci-P had a significant direct positive effect on ?Bray-P in new paddy field; ?HC-P and ?Ca-P had a significant direct positive effect on ?Bray-P in medium-term paddy field, and ?En-P had a significant direct positive effect on ?Bray-P in old paddy field.【Conclusion】Although exogenous P addition can significantly increase the components of the bioavailability of P in paddy soil, the emergence stage of the maximum increment bioavailability of P in paddy soil is different. Therefore, it is of great significance to timely and appropriately apply P fertilizers for the improvement of P fertility and the risk control of P loss in paddy fields.