The invention relates to composite nutritional oatmeal and a preparation method thereof. The composite nutritional oatmeal employs a composite cereal composition, a composite nutritional agent, butter and the like as main raw materials, and is prepared by seasoning. The composite cereal composition comprises one or more of rice, wheat, sorghum, corn, black rice, oat and buckwheat, and the composite nutritional agent comprises one or more of pollen, spirulina, tomato powder, blueberry powder, blackcurrant powder, vitamins and protein. The composite nutritional oatmeal possesses the composite fragrance of sea sedge, corn and tomato, is abundant in vitamins, pollen polysaccharide, mineral matters, vitamins and the like, has the effects of resisting fatigue, reducing fat, resisting radiation and the like, and satisfies health demands of people on flavor and nutrition. Additionally, the composite nutritional oatmeal employs an extrusion puffing technology and relatively well keeps nutrients in the raw materials and good brewing property.