The invention belongs to the field of dairy product processing, and discloses a sleep-promoting dairy product and a preparation method thereof. The dairy product is prepared from skim milk, bovine whey protein concentrate powder, rapeseed oil, L-theanine, gamma-aminobutyric acid, millet flour, honey, fructo-oligosaccharide, galactooligosaccharide, composite vitamins, composite minerals, a composite stabilizer and other raw materials through the steps of material melting, volume metering, homogenization, sterilization and the like. Through mutual cooperation of multiple nutritional ingredients,the prepared sleep-promoting dairy product can regulate the substance balance in a human body to promote sleep and improve the sleep quality. The dairy product is suitable for any person to eat, especially for people with sleep disorder to eat, and the preparation method is used for preparing the sleep-promoting dairy product.