The decoding of the human genome is not sufficient for a comprehensive understanding of the biological functions of the human body, but must take into account the impact of the microorganisms that accumulate on the human surface and in the human body and live in symbiosis with humans for a long time. The role of gut microorganisms in the development of human diseases is gaining increasing attention, and it is still unclear whether altered gut microecology is the initiator of disease or a consequence of disease. Ulcerative colitis (UC) is a chronic non-specific inflammatory disease of the rectal and colonic mucosa of unknown etiology. The disease is usually recurrent and persistent, and there is still no specific clinical treatment available. Recent studies have suggested that a combination of intestinal microorganisms and their metabolites, host genetic susceptibility, and imbalance in the natural or acquired immune response of the host intestinal mucosa are involved in the pathogenesis of IBD. The differences in gut microbial species and abundance between UC patients and healthy individuals have been demonstrated in many studies, and gut microbial diversity is significantly lower in UC patients compared to healthy populations. The composition and number of intestinal microorganisms in the human population have been altered, and the following are the more consistent findings: 1. the content of the dominant flora in the intestine is significantly reduced; 2. the overall diversity and stability of intestinal microorganisms are generally reduced; 3. the content of probiotic species such as Lactobacillus and Bifidobacterium is reduced; 4. mucosa-associated microorganisms have a more direct effect on the human host, while the microorganisms in fecal samples determine the metabolic products of intestinal microorganisms. products, with no significant differences in microbial composition and numbers between the two.