There are many clinical causes of dark tongue, and stomach cancer is one of them. In the early stage of stomach cancer, the tongue may become dark with stomach discomfort. However, black tongue moss is not necessarily the cause of gastric cancer, there are other reasons. Black moss is a rare clinical sign of the tongue, which is a symptom of the development of multiple systems and diseases. According to Chinese medicine, diseases of internal organs can be directly or indirectly linked to the tongue through meridians, and black moss can appear. Patients with gastrointestinal dryness and heat, damp-heat internalization, and cold-damp internalization may have black moss. In addition, black moss is mostly associated with mycotic infections and is also likely to occur with prolonged, high-dose antibiotic use. In addition to the above pathological reasons, physiological reasons including eating food that can be easily colored can also make the tongue moss black, which is a normal situation, after changing the diet, the color of the tongue moss can slowly return to normal. Patients should maintain a good diet and rest habits, combine work and rest; eat a reasonable diet, which is soft and nutritious, and reduce the intake of junk food; pay attention to the regulation of emotions, avoid stress and emotional tension, pay close attention to the tongue and body discomfort, and if necessary, go to the Chinese medicine department of the hospital for consultation.