A new use of Lactobacillus paracasei subsp. paracasei K56 capable of regulating the gastrointestinal flora balance is described. The deposit number of the Lactobacillus paracasei subsp. paracasei is DSM27447. This strain alone has the ability to significantly promote the growth of intestinal Bifidobacterium and Lactobacillus, suppress Desulfovibrio and/or Enterobacteria in the intestine, suppress Helicobacter and/or Escherichia-Shigella, and can endure a simulated in vitro gastrointestinal fluid stress environment. Experiments in mice show that this strain has no acute oral toxicity, no antibiotic resistance, and may be safely used in food processing.