The invention discloses a diamond / Si (Al) composite preparation technological method by a vacuum infiltration method, which belongs to the field of electronic packaging materials. The method is characterized by comprising steps: the vacuum infiltration method is adopted to mix silicon powder, aluminum powder and an organic binder according to a proper proportion, and being wetted to a paste by using an organic solvent is carried out; then, diamond particles are added, uniform stirring is carried out, uniform mixing by using a mixer is carried out, and a porous prefabricated billet with a regular shape is pressed; degreasing treatment is then carried out and the organic binder is decomposed completely; the porous billet is then put in a vacuum infiltration furnace and is buried by the silicon powder, sealing and vacuuming are carried out, the temperature rises above the melting point of silicon, liquid infiltration is carried out, compactness of the porous billet is realized, and a diamond / Si / Al composite with a regular shape, high compactness and excellent thermal physical properties can be prepared. The composite is a potential matrix material for electronic packaging, and has theadvantages of high thermal conductivity, low expansion, low density, high lightness, easy preparation, and little later processing difficulty.