The invention relates to an oat and linolenic acid composite beverage, relates to a preparation method of the beverage, and belongs to the technical field of processing of other beverages. The oat and linolenic acid composite beverage is mainly prepared from the following raw materials in percentage by mass: 1-6% of oat, 1-8% of linseed oil, 2-3% of maltose, 0.2-0.6% of fructo-oligosaccharide, 1-3% of xylitol, 1-4% of cane sugar or starch syrup, 2-6% of coconut milk, 0.1-0.3% of a composite emulsion stabilizer, 0.005-0.01% of edible essence and 0.1-1% of sodium ascorbate. According to the oat and linolenic acid composite beverage disclosed by the invention, the oat is used as a main raw material, the linseed oil and the coconut milk are added, the specific composite emulsion stabilizer is matched, and a specific technology is used, so that the oat and linolenic acid composite beverage is prepared. High omega-3 fatty acid content of the oat beverage is guaranteed, and besides, a good stabilizing effect can be achieved. Under normal temperature, after being subjected to standing for 3 months, the oat and linolenic acid composite beverage does not generate precipitates, and is free of a layering phenomenon and the phenomenon that fat floats upwards.