Black moss is a rare clinical sign in pediatrics, and there are various causes of black moss. The situation is mild or severe, generally divided into 3 major categories. 1, is a sign in the development of multiple diseases of multiple systems, mostly seen in the serious stage of the disease. Chinese medicine considers the tongue moss gray and black, the main internal disease, the condition is generally more serious. It may be extremely hot or cold. If the moss is grayish black and smooth, and the tongue is pale white, it is Yang deficiency with internal cold or cold dampness inside; if the moss is grayish black; the dry tongue is red and vivid, it is heat extremity and yin injury, and clinically it is mostly transformed from yellow or gray moss. Most of the changes in the disease have reached a certain level, either heat or deficiency to the extreme. 2, clinically known as “black hair tongue”, by the excessive proliferation of filiform papillae, its keratinized part does not fall off and the formation of fluffy moss, black, green-black or brown. The former is abnormal development, and the latter is thought to be related to fungal infection. Black hairy tongue generally does not leave traces after healing, but because the cause is unknown, it is best to go to dentistry. 3, the situation is caused by some food staining, such as sour plum, black sesame paste, etc., or drugs, such as compound licorice tablets, iron, etc. also tend to stain the tongue black, which is only a temporary phenomenon, no need to worry. Since black moss is partly caused by more serious diseases in clinical practice, it is a manifestation of cold and hot evidence developed to the extreme. At the same time, when the condition worsens, black moss will also appear, which is a sign of critical condition, so the appearance of black moss in babies needs to be paid great attention to, and should go to the hospital in time to see a doctor.