To master the adsorption mechanism of dodecyl phosphoric acid (DDPA) and dodecyl phosphate (DPA) on the (001) and (001 ̅) surfaces of kaolinite. Through density functional theory (DFT), the adsorption configurations of DDPA and DPA on the (001) and (001 ̅) surfaces of kaolinite, the analysis of differential electron density, the charge transfer analysis of each bonding atom by Mulliken population, and the density of states analysis were studied and analyzed respectively, and flotation experiments were carried out for verification. The simulation results show that the adsorption energy of DDPA and DPA on the (001) surface of kaolinite is much stronger than that on the (001 ̅) surface of kaolinite. According to the Mulliken bond population results, it indicates that DDPA forms effective hydrogen bonds on both the (001) surface of kaolinite and the (001 ̅) surface of kaolinite, while DPA only forms strong hydrogen bonds on the (001) surface of kaolinite. The flotation results show that when the reagent concentration is lower than 1 mmol/L, DPA has a significant difference in the recovery performance of kaolinite and quartz of 125-75 μm, DPA is more likely to selectively adsorb on the surface of kaolinite than DDPA, and in the kaolinite-quartz mixed mineral system, when the mineral particle size is 125-75 μm, the selective adsorption effect of DPA on kaolinite is better, which is consistent with the theoretical results. Also, because the coal slime water produced during the wet coal washing and processing in the industrial process contains a large number of fine particles of kaolinite and quartz, it becomes possible to separate kaolinite in the coal slime water using DPA as a collector.