In recent years, the intestinal flora has become a research hotspot, and a large amount of evidence indicates that the intestinal flora imbalance is closely related to the occurrence and development of various diseases, especially the colorectal cancer (CRC). Intestinal flora disturbance exerts carcinogenesis by inducing chronic inflammation, DNA damage in epithelial cells, immune abnormalities, and production of intestinal flora metabolites and bacterial enzymes. With the development of high-throughput sequencing technology and metagenomic sequencing technology, our understanding of the relationship between gut microbiota and CRC has reached a remarkable level by constant breakthroughs. Intestinal flora can be used as biomarkers for the early diagnosis and prognosis of CRC, and affects the efficacy of immunotherapy and radiotherapy or chemotherapy, and provides a large number of potential targets for targeted therapy of CRC. Here, the authors review the research progress on the role of intestinal flora in the aspects of occurrence, development, diagnosis and treatment of CRC, aiming to provide reference for clinical praxis and basic research.