The vacuum filtration of hematite slurries and flocculated hematite slurries with anionic, cationic, and nonionic polyacrylamides was investigated. Test results show that the flocculated filter cake generally contains higher residual water than the unflocculated cake. Measurements of flocculants adsorption on a hematite surface, zeta potential, and contact angle of the mineral surface were carried out; the filter cakes were analyzed with a microscope and image analyzer; and the structure of the filter cakes was studied from the viewpoint of fractal theory. The existence state of residual water in flocculated filter cake was discussed. It was pointed out why a flocculated filter cake generally has a higher residual moisture content.