To investigate the distributions and stocks of different phosphorus (P) forms in marsh soils in Shanyutan of the Min River estuary, the Phragmites australis marsh (PA), Cyperus malaccensis marsh (CM) and ecotonal marsh (P. australis-C. malaccensis marsh,PA-CM) were studied. The results showed that easily decomposed phosphorus (Resin-Pi, NaHCO₃-Pi and NaHCO₃-Po) in total phosphorus (TP) were 48.3%-51.1%, followed by moderately decomposition phosphorus (NaOH-Pi, NaOH-Po, Sonic-Pi, Sonic-Po) (37.4%-38.8%) and hardly decompose phosphorus (HCl-P and Residual-P) (11.5%-12.9%). The contents of easily decomposed phosphorus, moderately decomposed phosphorus, and hardly decomposed phosphorus forms in soils of PA-CM significantly increased by 10.6%, 19.2% and 22.6% compared with those in soils of PA, while increased by 1.6%, 11.5% and 16.6% compared with those in soils of CM, respectively. The reasons for it should be attributed to the alterations of physical and chemical properties in soils of PA-CM such as grain composition, pH, Fe and Al contents during spatial expansion. The spatial expansion of PA and CM also changed the contents of TP and the stocks of P in soils of PA-CM. Compared with PA and CM, the levels of TP in soils of PA-CM increased by 20.0% and 7.1% and the stocks of P increased by 12.0% and 18.0%, respectively. This paper found that the spatial expansion of PA and CM not only altered the distributions and stocks of phosphorus forms in marsh soil, but also changed the transformation of different phosphorus forms. The distributions and stocks of phosphorus forms in the soils of ecotonal marsh were favorable for alleviating the competitive pressure of phosphorus for P. australis and C. malaccensis during their spatial expansion, which, to some extent, might maintain the stability of the ecotonal marsh ecosystem.