The invention discloses a composition for improving the intestinal microecology and preventing a chronic disease. The composition is prepared from inulin, galactooligosaccharide and composite dietary fiber, wherein the ratio of the inulin to the galactooligosaccharide to the composite dietary fiber is (1 to 75) to (1 to 75) to (5 to 95), and preferably (10 to 50) to (10 to 50) to (25 to 50). The invention further discloses balanced nutrition food containing the composition. The balanced nutrition food comprises cereal meal; and the ratio of the cereal meal to the composition is (50 to 95) to (50 to 5), and preferably (70 to 95) to (30 to 5). The composition can retain moderate survival of non probiotics through common glycan; a functional glycan prebiotics combination can promote growth of probiotics; and by the synergistic effect among glycans, stable equilibrium of intestinal microorganisms can be maintained, the intestinal flux, endotoxins and inflammatory factors are reduced, the immunity is enhanced, and the chronic disease is prevented. The balanced nutrition food can provide balanced nutrition for superorganisms, improve the subhealth and prevent the chronic disease.