The cause of long-term dry mouth is very complex, the most direct reason is that the salivary gland secretion function is affected, that is, the source of water is insufficient to cause. There are many reasons for the decline in salivary secretion function, as follows: 1, the most common head and neck malignant tumors after radiation therapy, radiation therapy on the salivary glands function irreversible damage, no saliva secretion, resulting in dry mouth; 2, autoimmune diseases, such as common dry syndrome, can be substantial damage to the salivary glands, resulting in less secretion or no secretion of salivary glands; 3, other reasons, such as taking medications, the Heart disease patients sometimes take atropine, atropine inhibits salivary secretion, salivary secretion is inhibited can appear dry mouth. Different causes in the treatment of different methods, if there are dry mouth symptoms, we should pay attention to analyze the causes, according to the different causes to do the appropriate treatment and therapy.