The invention discloses a preparation method of sericite powder. The method comprises the following steps that 1, a raw material is subjected to primary processing; 2, distilled water, a potassium permanganate solution and a potassium nitrate solution are added into sericite scale to obtain a mixture; 3, the mixture is filtered to obtain filter residues; 4, distilled water is added into the filterresidues, and carbon dioxide and ammonia gas are introduced to obtain sericite size; 5, a silane coupling agent, a surfactant, a cation catcher and conditioning liquid are added into the sericite size, and a precipitate is kept; 6, the precipitate is calcined under a high temperature condition to obtain the sericite powder. According to the preparation method of the sericite powder, by introducing the carbon dioxide and the ammonia gas, the filter residues are fully crushed and dispersed, then the carbon dioxide and the ammonia gas are in cooperation with the silane coupling agent, the surfactant, the cation catcher and the conditioning liquid, impurities in the filter residues can be removed, effects of the impurities on the dispersity and the glossiness of sericite are avoided, and meanwhile, the dispersity and the dispersion evenness of the sericite powder are improved, so that the prepared sericite powder is fine and smooth in particle and high in glossiness.