The invention discloses a preparation method of three-dimensional porous silica powder, relates to a porous nanometer function material and belongs to the field of preparation of porous nanometer function materials. Silica powder with different purities fume is taken as a raw material, and metal nanoparticles (Ag, Au, Pd, Pt, Cu and the like) taken as catalysts are introduced on the surface of the silica Powder; in a reaction system with HF acid and an oxidizing agent, an MACE (metal-assisted chemical etching) method is adopted, and the porous silica powder with different pore structures and porosities is prepared under the room temperature condition. Compared with a traditional electrochemistry anode etching method, a magnesiothermic reduction method and the like, the method provided by the invention has the advantages of avoiding expensive single crystal silicon raw materials, harsh high-temperature reaction equipment and operation, being simple in equipment, easy in operation, low in cost, controllable in material structure and suitable for large-scale industrial production, and the like. The preparation method of the three-dimensional porous silica powder has wide application prospect in the fields of lithium ion batteries, photoelectric materials, biomedicine, sensors and the like.