Abstract: The effect of starch on the flotation of kyanite,quartz and biotite and the interaction mechanism theory were investigated by flotation tests,adsorption capacity measurements,zeta potential experiments and infrared spectroscopy analysis.The pure mineral flotation experimental results show that the flotation of kyanite was inhibited by starch in the presence of dodecylamine as cationic collector when the pH of 6.5.When the concentration of starch was 22.5mg/L,the flotation recovery of kyanite was 2.78%.The results show that the starch is an effective modifier in reverse flotation separation.The starch was absorbed to mineral surface of kyanite except electrostatic force,which can also with mineral surface of Al³⁺ in cooperation with chemical bonds.The starch was absorbed to the surface which caused kyanite mineral surface being hudrophilic,and starch played good depression effect.And starch and dodecylamine can compete adsorbed on the surface and decrease of kyanite adsorption quantity of collecting agent on mineral surface.