The invention discloses a ketogenic diet formula milk and a preparation method thereof and aims to solve the technical problem that convenience is provided for a patient to have food therapy through ketogenic diet. The ketogenic diet formula milk contains the following components per 100 g: 1.5-12.5 g of fat, 0-5 g of protein, 0-0.5 g of carbohydrate, 0-0.6 g of flavoring, 0-1.2 g of nourishing essence and the balance of liquid milk. The preparation method comprises the step of uniformly mixing fat, protein, carbohydrate, flavoring, nourishing essence and the liquid milk according to the prior art. Compared with the prior art, the ketogeic diet formula milk takes human milk and animal milk of which metabolizable sugar is removed as the main raw material, adopts a nutrient formula close to physiological needs, has a good mouthfeel, is easily accepted by the patient, is convenient to take, is suitable for treating epilepsy, diabetes, all kinds of tumors, behavior disorder, autism, brain and spinal cord injuries, and adiposity, and is also suitable for normal people to lose weight and change the structure of the main nutrients of the body, as well as for animal experiments.