The invention discloses a composition for improving intestinal microecology and preventing chronic diseases, which comprises inulin, galacto-oligosaccharide and compound dietary fiber, wherein the ratio of inulin, galacto-oligosaccharide and compound dietary fiber is: 1-75: 1~75:5~95, the optimal ratio is: 10~50:10~50:25~50. The invention also discloses a balanced nutritious food containing the composition, which includes grain powder, and the ratio of the grain powder to the composition is: 50-95:50-5, and the optimal ratio is: 70-95:30- 5. The present invention maintains the proper survival of non-probiotics through ordinary polysaccharides, the combination of functional polysaccharides and prebiotics promotes the growth of probiotics, maintains the homeostasis of intestinal microorganisms through the synergistic effect between polysaccharides, and reduces intestinal flux, endotoxin and Inflammatory factors, enhance immunity, prevent chronic diseases. The balanced nutritional food of the invention provides balanced nutrition of super organisms, improves sub-healthy physique, and prevents chronic diseases.