The gut microbiota is considered an indispensable organ and plays an important role in human health. Numbers of diseases ranging from chronic inflammatory, metabolic diseases to neurological disorders and cancer were associated with the compositional and functional changes in the gut microbiota. Cancer immunotherapy such as immune checkpoint inhibitor (ICI) is an emerging treatment with high specificity and efficacious. Recent studies showed that the efficacy of ICIs in patients with cancer was associated with the gut microbiota. In this review, we summarized studies on cancer immunotherapy⁃associated gut microbes, including the function of the gut microbiota in cancer immunotherapy, the potential mechanisms on how it affects the cancer immunotherapy. For example, metabolites and surface proteins of gut microbes could inhibit tumor growth or induce the apoptosis of tumor via direct or indirect mechanisms, or modulate the immune system especially in the tumor microenvironment. The development of bioinformatic tools and statistical approaches along with the application in the analysis of gut microbiota accelerated the discovery of new gut microbes associated with cancer immunotherapy. Up to now, there are several organizations and pharmaceutical companies involving in the development of live biotherapeutic products targeting cancer immunotherapy. Numerous clinical trials have been registered and launched based on the fundamental researches on gut microbiota. In this review, we also summarized the computational methods for identifying candidate therapeutic bacterium, as well as the development of live therapeutics on cancer immunotherapy. We also discussed the challenges of current live therapeutics discoveries on cancer immunotherapy and prospective development trends.