The invention discloses a preparing method of aluminium alloy casting moulding sand. New quartz roughing sand, used quartz roughing sand, zircon sand, electrolytic aluminium slag powder, hollow microspheres and a binder are adopted as components of the moulding sand, wherein the binder is novel in design and is prepared by blending starch, furan resin, calcium bentonite, bagasse cellulose powder, zinc stearate and sodium tripolyphosphate, and steps and parameters of the preparing method are optimized according to the components of the moulding sand. Therefore, the prepared moulding sand has characteristics of good refractoriness, high gas permeability, good collapsibility, and capability of reducing casting defects and making casting surfaces clean and smooth. By adoption of the moulding sand for casting aluminum alloy castings, the rate of defects comprising sand burning, air holes, cracks, cold shut, shrinkage cavity, looseness, and the like is lower than 3%, the yield of finished product of the castings is largely increased and the casting cost is reduced.