The invention provides oat milk and a preparation method thereof. The oat milk is characterized by comprising the following components according to the part by weight: 20 to 70 parts of oat enzyme hydrolysis solution, 30 to 80 parts of milk, 0 to 0.5 part of stabilizing agent, 0 to 3 parts of white granulated sugar, 0 to 2 parts of polyglucose, 0 to 2 parts of high fructose corn syrup, 0 to 1.5 parts of honey, 0 to 1.5 parts of maltodextrin, 0 to 1 part of fructo-oligosaccharide, 0 to 1 part of galacto-oligosaccharide syrup, 0 to 1 part of wheat germ powder, and 0 to 0.5 part of salt. According to the invention, easily-absorbable oat enzyme hydrolysis solution is added in milk, so that double nutritions of oat and milk are combined perfectly, and then nutrition requirements and psychological requirements of modern consumers on living are met.