Abstract: This study aims to explore the effects of different types and amounts of carbon-based fertilizers on the phosphorus form distribution and transformation in coastal saline-alkali soil. A field experiment was set in Dafeng, Yancheng, Jiangsu Province, China. Four treatments were set as no fertilization (CK), straw carbon and chicken manure organic fertilizer (T1), rice husk carbon and chicken manure organic fertilizer (T2), coal carbon and chicken manure organic fertilizer (T3). Five kinds of soil volume ratios (4%, 6%, 8%, 12%, and 16%) for each carbon-based fertilizer treatment. The Hedley phosphorus classification by Tiessen was used to determine 9 kinds of phosphorus in soil. A systematic analysis was made to clarify their effects on the availability of phosphorus and the transformation relationship between phosphorus components in the saline-alkali soil in coastal beaches. The results showed as follows: 1) Different fertilizer ratios of T1, T2, and T3 treatments all reduced the pH and EC values of the saline-alkali soil in coastal beaches, compared with the CK. The three treatments of the carbon-based fertilizer shared the best effect on the ryegrass growth at a 12% fertilizer ratio. T3 treatment had the best effect with a 37.2% increase in the plant height and 29.8% increase in the root length. 2) There was no significant change in the soil total phosphorus (TP) content. But there was a significant increase in the soil available phosphorus (AP) and alkaline phosphatase (ALP) activities (P<0.05). The activity of the AP and ALP increased 345.1% and 106.9%, respectively, compared with the 12% fertilizer soil treated with the T3. 3) Three kinds of carbon-based fertilizers were promoted for the conversion of the medium active phosphorus components (NaOH-Pi, and NaOH-Po) and stable phosphorus components (D.HCL-Pi, C.HCL-Pi, C.HCL-Po, and Residual-P), compared with no fertilizer (CK). There were the active phosphorus components (Resin-Pi, NaHCO3-Pi, and NaHCO3-Po). The proportion of the active phosphorus in soil under T1, T2, and T3 treatments increased by 126.2% to 483.8%, 125.0% to 428.6% and 123.1% to 253.3%, respectively. The 12% fertilizer treatment was better than the rest treatments. Correlation analysis showed that the NaOH-Pi was negatively correlated with the NaHCO3-Pi, NaHCO3-Po, AP, and ALP, whereas the C.CL-Pi was negatively correlated with the NaHCO3-Pi and NaHCO3-Po. The structural equation model showed that the salinity (pH, EC) and ALP activity were the key influencing factors on the transformation of the soil phosphorus. In summary, the coal-based carbon chicken manure (T3) shared the best performance to improve the phosphorus availability of the saline-alkali soil in the coastal beaches. And 12% fertilizer ratio was suitable for application. The findings can provide the theoretical basis and practical reference to improve the availability, distribution, and transformation of phosphorus in the saline-alkali soil.