The intestinal flora is the normal microecosystem of the gastrointestinal tract. The intestinal flora has great complexity, and plays crucial roles in nutrient intake, host metabolism, endocrine signaling, homeostasis and immune regulation. Disorders of the intestinal flora can lead to an out-of-balance in immune system, and even results in an increased risk of diseases, including the occurrence and development of malignant tumors. Accumulating evidence shows that intestinal microorganisms may assist in systemic therapy by increasing the heterogeneity of the tumor, thereby promoting anti-tumor therapy. Targeting intestinalflora during the treatment of cancer has shown good efficacy. This review focuses on recent advances in research about intestinalflora, the relationship with tumor development, and the potential anti-tumor effects.