Twenty-seven surface sediment samples collected from the Changjiang Estuary in February 2009 were sequentially extracted to study the forms of phosphorus (P) and their ecological risks as internal P sources. It is shown that the content and distributions of P in surface sediments are majorly controlled by the sourses of P and the grain size of sediments. Ex-P (Exchangeable P), Fe-P (Fe-bound P), Al-P (Al-bound P), Lea-OP (Leachable Organic P), and CFA-P (Authigenic Carbonate Fluoapatie) are transferable phosphorus forms, which could be released from sediments to seawater and return to the biogeochemical cycling. Transferable P accounts for 15-43% of TP in sediments. Among the transferable P forms, Fe-P is the largest form in content, accounting for 45.5% of total transferable P; and the other forms are in the order of Al-P>CFA-P>Ex-P>Lea-OP. The single factor contaminant index of transferable P indicates low ecological risks of sedimentary P release. The ratios of iron to phosphorus in the sediments (TFe∶ TP) and in BD extractant (BD-Fe∶ BD-P) are above 27 and 20, respectively. This suggests that the surface sediments have sufficient sorption sites for dissolved P to adsorb onto them,and also have high capacity to retain particulate P in sediments. Consequently, P has the potential to migrate from water to sediment in the Changjiang Estuary, and sedimentary P release has low risks to eutrophication.