Provided is a device for preparing a large-sized high-quality aluminium alloy ingot, which is mainly composed of a uniform cooler, a hot top, an oil-gas lubrication mold, an induction coil and a dummy ingot, wherein the hot top is arranged above the oil-gas lubrication mold, the induction coil is arranged outside the oil-gas lubrication mold, the uniform cooler is arranged inside the oil-gas lubrication mold, and the dummy ingot is arranged below the oil-gas lubrication mold. Further provided is a method for preparing a large-sized high-quality aluminium alloy ingot. The device combines a partitioned gas supply mold with the uniform cooler and an electromagnetic stirrer, and the effective coupling of the three achieves forced and uniform solidification forming of a melt under gas pressure contact conditions, such that a stable and continuous gas film is formed between the melt and the mold. The ingot has a smooth surface, and a fine and uniform internal structure.