The invention provides a preparation method for a plate for an aluminium alloy carriage. The preparation method comprises the following contents that: (1) the plate for the aluminium alloy carriage comprises the following components: 0.05 to 0.4 weight percent of Si, 0.15 to 0.45 weight percent of Fe, 0.03 to 0.15 weight percent of Cu, 0.3 to 0.6 weight percent of Mn, 4.6 to 5.8 weight percent of Mg, 0.03 to 0.15 weight percent of Cr, 0.01 to 0.03 weight percent of Ti, and the balance of Al and unavoidable impurities; (2) a manufacturing method comprises the following steps: taking aluminium ingots, aluminium intermediate alloy ingots, magnesium ingots, a manganese agent, a copper agent and a chromium agent as raw materials; performing low liquid level casting after smelting, preserving heat, degassing, and double-stage deep bed filtering are performed; and performing the processes of sawing and surface milling, heating, hot rolling, cold rolling, cleaning, annealing, stretching and straightening, and transversely shearing to obtain the plate for the aluminium alloy carriage. The obtained plate for the aluminium alloy carriage has high strength, a flat and neat plate shape, and good corrosion resistance, good bending machining performance and welding performance.