The invention discloses a preparation method of a high-aluminum content, alkali-free and chlorine-free setting accelerator. The preparation method comprises the following steps: (1), uniformly mixing2-acrylamide-2-methylpropanesulfonic acid, acrylamide, acrylic acid, sodium hydroxide, an initiator, a crosslinking agent with water to obtain an aqueous phase; uniformly mixing cyclohexane with sorbitan oleate to obtain an oil phase; heating the oil phase to 50-70 DEG C, then dropwise adding the aqueous phase, performing a polymerization reaction for 5-10 hours, then filtering and drying to obtain a dissolution promoter; (2), uniformly mixing aluminum sulfate, the dissolution promoter with water, standing still for 1 h, continuing to add alcohol amine, a pH regulator and a rheological agent,then heating to 60-80 DEG C, reacting for 3-6 h, and cooling to room temperature to obtain the high-aluminum content, alkali-free and chlorine-free setting accelerator. According to the preparation method, through use of the dissolution promoter, the content of the aluminum sulfate is increased; the alkali-free ad chlorine-free setting accelerator prepared through modification can greatly improvethe 1d compressive strength of cement mortar and can improve comprehensive performance, such as the stability and the like, of a product.