The invention discloses a synthesis method of an MFI molecular sieve nanosheet. The method takes a small amount of template agent, silicon source and aluminum source as raw materials for hydrothermal synthesis, and is characterized by comprising the following steps: firstly, uniformly stirring the template agent, the silicon source and a certain amount of water, then selectively adding the aluminum source, adjusting the pH value of the system, stirring and pre-crystallizing for 1-50 hours at 40-100 DEG C, and then crystallizing for 1-10 days at 80-150 DEG C; and after the crystallization is finished, cooling the reaction kettle to room temperature, and then carrying out suction filtration/centrifugation, washing and drying on the product. According to the method, the synthesis temperature is low, the synthesis pressure is low, a fluorine-containing reagent does not need to be used, the yield exceeds 80%, and the thickness of the nanosheet can be regulated and controlled through the pH value of the system and the dosage of a template agent. The synthesized MFI molecular sieve nanosheet is high in crystallinity and controllable in thickness, more synthesis energy consumption is saved under the low-temperature and low-pressure conditions, industrial scale-up production is facilitated, and the MFI molecular sieve nanosheet has a good industrial popularization prospect.