Malnutrition among cancer patients usually induces adverse consequences such as increased postoperative complications, decreased quality of life and increased mortality. According to the location of tumor, its incidence ranges from 40% to 80%, so it is very important to reduce malnutrition among cancer patients. Cancer⁃related malnutrition is closely related to the high energy consumption of the tumor itself, cancer⁃related anorexia and the side effects of cancer treatment. At present, tumor specific enteral nutrition agents do not eliminate the risk of malnutrition. Healthy intestinal microbes have high diversity, complex and stable structure, and are capable of resisting external environmental pressure. In contrast, non⁃healthy people show decreased bacterial diversity, loss of resistance to external environmental pressure, intestinal microecological disorders and other adverse conditions, such as cancer patients are often accompanied by the decline of intestinal microbiota, diversity and the proportion of beneficial bacteria in the process of disease,which seriously affects the immune ability and appetite of the body. As an important microecological agent, probiotics have the functions of regulating immune system function, energy metabolism and preventing colorectal cancer, which have a beneficial impact on human health. It can be predicted that probiotics may have a positive impact on the nutrition of cancer patients by regulating the structure and composition of intestinal microbiota, the secretion of cytokines, gastrointestinal peptides and other media, improving food intake and intestinal nutrition absorption. This paper systematically discusses the characteristics of intestinal microbiota and the potential role of probiotics in malnourished cancer patients, and puts forward the application prospect.