The invention provides a method for synthesizing an AFI type SAPO (silicoaluminophosphate) molecular sieve. The method comprises steps as follows: (1), initial reactants including a special reaction medium, an aluminum source, a silicon source, a phosphorus source and hydrofluoric acid are mixed uniformly in a mortar, and are ground manually for 10-20 min; (2), a mixture obtained in the step (1) is transferred to a reaction vessel and heated to be in a molten state, and a precursor mixture is obtained; (3), the precursor mixture obtained in the step (2) is subjected to normal-pressure crystallization under microwave radiation for 10-120 min at the crystallization temperature of 150-180 DEG C; (4), the mixture is naturally cooled to the room temperature after the crystallization, and is centrifugally washed with deionized water and acetone in sequence until a supernatant is clarified, then a product is dried for 100-150 min at the temperature of 110 DEG C, and raw molecular sieve powder is obtained; (5), the raw molecular sieve powder obtained in the step (4) is roasted at the temperature of 550 DEG C for 1-5 h, and the AFI type SAPO molecular sieve powder with high silicon content is obtained.