The common reasons for spitting black sputum include long-term smoking, caused by environmental factors, bleeding in the lungs and so on. 1. Long-term smoking: cigarettes contain a lot of tar, nicotine and other substances, long-term smokers will make these substances deposited in the mucous membrane of the trachea bronchus, coughing, will be discharged with the sputum, the phenomenon of black sputum. 2. Environmental factors: often in the smoke, dust, haze more work and life in the environment, these foreign bodies will easily be inhaled, when coughed up with sputum, will also cause black sputum. 3. Bleeding in the lungs: Commonly found in patients with tuberculosis, lung cancer and bronchial dilatation, when active bleeding stops, there will be a small amount of blood stagnation in the lungs. When coughing, this blood sludge will be discharged with sputum and black sputum will appear. Spitting black sputum, there may be other reasons, such as upper gastrointestinal bleeding, blood with the sputum spit out, the patient should go to the hospital in time to do the appropriate examination and symptomatic treatment.