The invention provides a preparation method for near-eutectic aluminium-silicon alloy semisolid slurry or blanks. The method comprises the steps of Step 1, preheating alloy aluminium-silicon ingots, adding into a crucible resistance furnace, after the alloy aluminium-silicon ingots are molten, stirring for degassing, refining, performing first standing, cooling, skimming, performing second standing, thus obtaining an alloy liquid; Step 2, preheating a mechanical roller coated with a casting coating inside; Step 3, inclining the mechanical roller relative to the horizontal ground, injecting the alloy liquid into the mechanical roller through a quantitative pouring system, transferring the alloy liquid into a tundish with a temperature control system, standing, and performing high-pressure extrusion casting to obtain the near-eutectic aluminium-silicon alloy semisolid slurry; Step 4, pouring the near-eutectic aluminium-silicon alloy semisolid slurry into metal molds directly, and solidifying, so that the near-eutectic aluminium-silicon alloy semisolid blanks can be obtained. According to the method, the slurry producing efficiency is high, high-performance castings can be prepared, and the method is high in market promotion value.