Abstract: The intestinal microecology (IM) is the largest and most important microecological system of the human body, and is a key factor in activating and maintaining intestinal physiological functions. An increasing number of studies have investigated the effects of intestinal microorganisms on various tissues and organs and elucidated their relationships with various diseases. These findings are gradually being translated into clinical practice. Intestinal microorganisms impact the occurrence, progression, treatment response, and toxic effects of tumors. Detailed studies investigating correlations between IM and tumors have opened a new chapter in IM research, driven by methods and technologies including next generation sequencing (NGS) and bioinformatics. The IM maintains host immune system functions and plays key roles in response to tumor-controlling drug therapy. Increasing evidence indicates that tumor control drug efficacy depends largely on IM balance, and strategies based on advances in understanding IM show promising application prospects for tumor diagnosis and treatment.