The invention specifically relates to a preparation method for a high-proportion AEI/CHA (SAPO-18/SAPO-34) eutectic molecular sieve, which belongs to the field of auxiliary chemicals. The preparation method comprises the following steps: dissolving dry pseudo-boehmite powder in distilled water, adding a phosphoric acid solution and then successively adding silica sol, N,N-diisopropylethylaine and triethylamine so as to obtain a mixed solution; and uniformly stirring the mixed solution, then carrying out constant-temperature crystallization, centrifugally washing a product obtained after crystallization with distilled water until the product is neutral and then carrying out drying and roasting so as to obtain the final product high-proportion AEI/CHA eutectic molecular sieve. The method has the advantages of mild synthesis conditions and low preparation cost; and the proportion of AEI (SAPO-18) constitutional unit in an AEI/CHA eutectic phase is high.