The flocculation behavior of ultrafine kaolinite suspension was investigated through settlement tests andFTIRmethod was employed to probe the adsorption mechanism of flocculant on kaolinite. The results show that the maximum settling rate of kaolinite occurs at pH value of 3.33, which is close to the point of zero charge(PZC) of kaolinite (3.5). This result is in good agreement with the double electric layer theory. Kaolinite suspension reaches the largest settling rate at a low concentration of 39 g/t for poly diallyl-dimethyl-ammonium chloride(PDADMA) flocculant, whereas for polyacrylamides(PAM) the dosage is required to be 500 g/t. When macromolecule polymer is adsorbed on surface, kaolinite particles may be flocculant due to the bridging effect. There are cation flocculant characteristic bands on the spectrum of kaolinite but no obvious shifting. Thus, the adsorption of poly diallyl-dimethyl-ammonium chloride on kaolinite surface is physical adsorption.