Solid polymeric ferric sulfate (SPFS) with excellent solubility and high basicity up to 20.16% was prepared employing hydrogen peroxide as oxidizer via acid deficient method. The transformation and size distribution of iron (III) species in the stock solution of SPFS (SPFSsto) were investigated, and coagulation behavior of iron (III) species in surface water was explored as well. It was found that the as-prepared SPFS with a high basicity was of high total iron content about 24.55% with an amorphous structure. The iron (III) species in SPFSsto suffered complicated behavior during aging and dilution, in which both further polymerization and depolymerization were included, the average diameters of iron (III) species in SPFSsto varied from 1 nm to 4 nm and decreased with the increase of R value at the total iron concentration of 1.0M, and became more dispersed at the total iron concentration of 1.0mM. The distribution of iron (III) species in surface water used in experiment depended on the initial pH value of the coagulation system and transformed during coagulation. In general, the low polymer of iron (III) species Fea dominated in acidic system, while the medium ones Feb and the high ones Fec dominated in neutral and basic systems, respectively. Charge neutralization and complexation by Feb species were found to be the most efficient mechanisms in removal of high molecular weight hydrophobic organics, and absorption and sweeping capabilities of Fec species dominated in removing low molecular weight hydrophilic organics.