The invention relates to a high-performance silicon carbide modified powder preparation method, which is used for slip-casting moulding. The preparation method uses a hydroxy carboxylic acid organic matter, tetramethylammonium hydroxide, and siloxane polyether to modify the silicon carbide powder through a two-step method. The method is characterized in that a modifier containing hydroxy carboxylic acid organic matter and tetramethylammonium hydroxide are fully mixed with the silicon carbide powder, and the mixture is subjected to ball milling modification, centrifugation and drying to obtainthe primary modified powder; the primary modified powder is prepared to obtain slurry with the solid phase content being 40-60 Vol%, polyether siloxane is added drop by drop for secondary modification, and the material is subjected to centrifugation and drying to obtain the final silicon carbide modified powder. The equipment in the method is simple, the preparation cost is low, and the preparation period is short. The prepared silicon carbide modified powder can be used for preparing the slurry with good stability, high solid phase content and low viscosity, at the same time, the modified silicon carbide powder with a pH value being 4-10 is prepared according to the practical slip-casting moulding.