Abstract: The human intestine is estimated to contain approximately 10 trillion bacteria, comprising around 500–1, 000 different species. These bacteria affect the digestion and absorption of human nutrients, influence the risk of infection and autoimmune diseases, and participate in the metabolism of drugs. The incidence and mortality rates of lung cancer are rising rapidly. Lung cancer is the most dangerous malignant tumor in humans. Researchers have found that the intestinal flora may affect the occurrence of lung cancer through metabolic or immune pathways. In addition, it can affect the efficacy of radiotherapy, chemotherapy, immunotherapy, and other treatments for lung cancer. However, the benefits varied among different patients. The role of intestinal flora in the occurrence, development, diagnosis, and treatment of malignant tumors has become a research hotspot in recent years. Therefore, this review summarizes the research on the correlation between intestinal flora and lung cancer.