Coagulation kinetics and floc properties are of great fundamental and practical importance in the field of water treatment. To investigate the performance of Fe(VI) and Fe(III) salt on particle coagulation, Malvern Mastersizer 2000 was employed to continuously and simultaneously monitor the kaolin floc size and structure change, and population balance modeling was used to investigate the coagulation mechanism. The results show dosage increase had positive effect on collision efficiency and floc strength and negative effect on restructure rate. Low shear rate resulted in higher collision efficiency and stronger floc. Low water temperature had a pronounced detrimental effect on coagulation kinetics. Temperature increase showed the most significant positive effect on collision efficiency, floc strength and restructure rate. The optimum pH zone for the coagulation was found to be between 6 and 8. Further pH increase lowered the collision efficiency and floc strength and increased the restructure rate. FeCl3 resulted in a larger ratio of the mass to volume of kaolin flocs (compactness) than those induced by ferrate.