The invention discloses a preparation method of a fluorinated cellulose nanocrystal lubricating grease thickening agent. The method comprises the following steps: dispersing cellulose nanocrystal into N, N-dimethylformamide, adding 4-dimethylaminopyridine and triethylamine, and carrying out ultrasonic dispersion to obtain a suspension; slowly dropwise adding a 2-bromoisobutyryl bromide solution into the obtained suspension in an inert atmosphere, heating to 70-90 DEG C after dropwise adding, reacting for 24-36 hours, centrifuging, washing and dialyzing to obtain CNC-Br powder; dispersing the CNC-Br powder into N, N-dimethylformamide, adding copper bromide, N, N, N, N, N-pentamethyldiethylenetriamine, cuprous chloride and a monomer with a fluorine-containing group, removing oxygen in a reaction system, and carrying out an atom transfer radical polymerization reaction in an inert atmosphere; and removing impurities, and drying the extracted product to obtain the product. According to the preparation method, surface hydroxyl groups of the cellulose nanocrystals are replaced by Br-containing ester groups, and then monomers with fluorine-containing groups are added, so that fluorinated chains grow on the surfaces of the cellulose nanocrystals for grafting, and the lubricating grease thickening agent with excellent performance is obtained.