Based on the analyses of crystal structures and surface properties of diaspore and kaolinite, an effective diaspore depressant, CPAM(cationic polyacrylamide) polymers was discovered by single minerals tests, separation experiments of artificial mixed minerals, zetapotential and adsorption measurement. The reverse flotation separation on diaspore and kaolinite can be carried out using collector dodecylamine acetate and depressant CPAM under pH 5.5-8.5. On the surfaces of diaspore, there are a large amount of active aluminum atoms. They can bond with-C(O)NH2 groups in CPAM and make the-CH2N+(CH3)3 groups in CPAM orient toward the outer surfaces of diaspore, which prevents a majority of the dodecylamine cations from adsorbing on diaspore, enhances hydrophilicity of diaspore, and depresses the floatability of diaspore. But for kaolinite, CPAM polymers have little effect on its floatability.