Abstract: In recent years, the role of intestinal flora in immune checkpoint inhibition has been widely recognized, and it is one of the research hotspots in immunotherapy. Current studies have shown that intestinal flora affects the final efficacy of immunotherapy by promoting the modulation of the body's immune system, shaping the tumor immune environment, and correlating with other immune biomarkers such as tumor mutational burden(TMB), tumor neoantigen burden(TNB), and microsatellite instability(MSI). Therefore, improving the efficacy of immunotherapy through accurate and effective intervention via the intestinal flora has become the focus of clinical intervention. At present, it is desirable to use antibiotics, fecal transplantation, oral probiotics, and other means to improve the efficacy of immune checkpoint inhibitors and reduce immune-related adverse reactions. However, the clinical practice still faces challenges. Thus, this review examines the relationship between gut microbiota and immune checkpoint inhibitor therapy.