The invention discloses a method for preparing a silicon nitride reinforced aluminium-based composite material, which comprises the following steps: performing wet ball milling and drying on 60 to 67.5 weight percent of silicon oxide, 22.5 to 30 weight percent of carbon black, 1 to 10 weight percent of alpha-Si3N4 seed crystal, and 1 to 10 weight percent of Y2O3 to prepare mixed powder, sieving and granulating the mixed powder, and forming a blank piece through mold pressing; heating the blank piece to 1,750DEG C under the condition that the nitrogen pressure is six times of atmospheric pressure, preserving heat for 2 hours, and sintering to obtain a porous silicon nitride prefabricated body of which the relative density is between 20 and 30 percent; putting the porous silicon nitride sintered body in a die cavity of a die casting machine, and heating the die cavity to the temperature of between 500 and 700 DEG C, or firstly separately preheating the sintered body to the temperature of between 500 and 700 DEG C and then putting the preheated sintered body to the die cavity of the die casting machine; simultaneously, heating aluminium alloy to a melting state, pouring the molten aluminium alloy into the die cavity in which the prefabricated body is arranged, and pressing the molten aluminium alloy into the porous silicon nitride prefabricated body through a press machine; and finally, taking an ingot out after cooling, and performing heat treatment to obtain the silicon nitride reinforced aluminium-based composite material.