Coughing up smelly sputum in late stage of lung cancer is usually caused by the combination of anaerobic bacteria infection. Anaerobic bacteria usually grow in anaerobic or low oxygen environment, and anaerobic bacteria infection is characterized by smelly secretions. In advanced stage of lung cancer, lack of oxygen may also cause anaerobic bacteria infection to grow and multiply, resulting in smelly sputum in coughing. Cancer patients with tumor breakdown are easily infected with germs, and patients often have fever, cough, sputum, dyspnea and other symptoms. Patients with smelly sputum in advanced stage of cancer usually need to do sputum smear examination and bacterial culture to confirm the diagnosis. Patients with sputum stinking in advanced stage of cancer should actively seek medical treatment, and patients should not use medication on their own to avoid adverse results; patients should be treated according to standardized treatment under the guidance of physician’s interview.