The invention discloses a method for synthesizing microporous molecular sieve by-product fluoride by means of fluosilicic acid. The method comprises the following steps that ammonia water is added to the fluosilicic acid, the temperature is increased to range from 30 DEG C to 45 DEG C for heat preservation reaction, the addition amount of the ammonia water is controlled to make pH of a system range from two to six when the reaction is completed, and filtrate and a filter cake are obtained after filtering separation is conducted; the ammonia water is continuously addedtothe obtained filtrate, the temperature is increased to range from 40 DEG C to 50 DEG C for reaction, the addition amount of the ammonia water is controlled to make the pH of the system larger than or equal to nine when the reaction is completed, and filtrate and a filter cake are obtained after filtering separation is conducted; the obtained filter cake serves as a silicon source, guiding agents and templating agents are added, and crystallization is conducted for 1-7 days at the temperature ranging from 165 DEG C to 175 DEG C by taking water as a dispersion medium; an obtained product is washed and dried after suction filtration is conducted, the dried product is roasted through a muffle furnace, and an MFI structural molecular sieve is obtained. According to the method for synthesizing the microporous molecular sieve by-product fluoride by means of the fluosilicic acid, low-price phosphatic fertilizer by-product fluosilicic acid serves as the raw material to prepare the MFI structural molecular sieve with high additional value through a two-step combination method, and fluorine ions are recycled and utilized to generate the fluoride, so that environmental pollution is reduced.