Lung cancer is a common malignant tumor worldwide with high incidence and mortality rates. Previous studies have claimed that the microbial community plays an integral role in the development and progression of lung cancer. Emerging evidence reveals that gut flora plays a key role in cancer formation and evolution by participating in mechanisms such as metabolism, regulation of inflammation and immune response. Not only the gut flora, but also the presence of intratumoral microbiota may influence lung cancer progression through multiple mechanisms. These research advances suggest that intestinal flora and intratumoral microbiota may not only serve as potential biomarkers for lung cancer, but may also be targets for therapy. However, current studies on both in lung cancer are still limited. Given this, this study aimed to systematically review the latest findings on the major bacterial species of the intestinal flora and their possible protective or harmful roles in the formation, progression, and metastasis of lung cancer. In addition, we analyzed the potential mechanisms by which the intratumoral microbiota affected lung cancer and elaborated on the potential roles of the gut flora and its metabolites, as well as the intratumoral microbiota, in modulating the efficacy of immunotherapy in lung cancer.