The invention relates to the field of liquid dairy product, in particular to a milk oligopeptide added liquid milk and a preparation method thereof. The milk oligopeptide added liquid milk, based on 1000 parts by weight, comprises 942-996 parts of milk, 0-50 parts of white granulated sugar, 3-5 parts of milk oligopeptide, 0.1-1.5 parts of thickening agent and 0.9-1.5 parts of emulsifying agent combination, wherein the emulsifying agent comprises 0.8-1.1 parts by weight of sucrose fatty acid ester with HLB value being 15 and HLB of total emulsifying agent being 9-11. The invention surmounts the technical difficulty that a quantity of milk scale is produced when adding high protein substance in superhigh temperature liquid milk, adds variety of liquid dairy products which are suitable for puerperae, rich in protein and Fe, and has high absorptivity and good mouth feel, and innovates the product structure and formula composition of original compound liquid milk, thus new product varieties appear on market.