The invention belongs to the field of aluminium alloy manufacturing, and particularly relates to a production method for an aluminium alloy slab ingot. The production method for the aluminium alloy slab ingot provided by the invention comprises the following steps: (1) starting N cold water pumps, wherein N is an integer greater than or equal to two; (2) enabling a second water utilization valve for producing a second aluminium alloy slab ingot to be in a closed state, and opening a first water utilization valve for a first aluminium alloy slab ingot; (3) when the ingot length of the first aluminium alloy slab ingot is greater than 600 mm, opening the second water utilization valve for the second aluminium alloy slab ingot, so that simultaneous production of the first aluminium alloy slab ingot and the second aluminium alloy slab ingot is realized gradually. According to the production method for the aluminium alloy slab ingot, one water supply meets the requirement on the simultaneous production of two ingots through the transformation of a cooling water control system and the scientific optimization of casting process conditions, so that the production efficiency of the aluminium alloy slab ingot is greatly improved.