The invention discloses a method for preparing modified pseudo-boehmite. The method is characterized by comprising the following steps: (1) sequentially adding activated aluminum oxide, aluminum hydroxide and modifying agents into a proper amount of deionized water under the fully stirring condition, wherein the total amount of the activated aluminum oxide and aluminum hydroxide accounts for 5-20 mass percent of the deionized water, the modifying agent(s) is/are selected from one or more of boron, fluorine, silicon, phosphorus, magnesium, titanium, zinc and zirconium, and the total amount of the modifying agents accounts for 0.1-10 mass percent of the deionized water; (2) performing homogenizing and refining pretreatment on the obtained slurry, thereby obtaining the slurry of which the average particle size is 0.2-20 microns; (3) adding an alkali to regulate the pH value of the pretreated slurry system to 8-11, transferring the materials into a high pressure reactor to carry out a hydrothermal reaction, controlling the reaction temperature to 100-250 DEG C, wherein the reaction time is 1-48 hours; (4) performing solid-liquid separation on the obtained slurry after the reaction is ended, and washing, thereby obtaining a product filter cake in which the impurities are removed; and (5) drying, and grinding, thereby obtaining the pseudo-boehmite powder.