The invention discloses a preparation method of a low-alkali liquid setting accelerator. A suspending stabilizer is prepared by copolymerizing acrylamide and an unsaturated acid, and the suspending stabilizer and an aluminate mother liquor undergo a composite reaction. A high-molecular copolymer is introduced to optimize the setting accelerator, so the coherency of the setting accelerator is improved, precipitates are effectively inhibited, the storage stability of the mother liquor is greatly improved, and the stability lasts for one year or more. A promoter is added after the copolymerization of the suspending stabilizer is finished, and the introduction of the promoter can improve the conversion rate of the copolymerization reaction and effectively control the initial setting time and the final setting time of the liquid accelerator.