Sweetness in the mouth may be a precursor manifestation of diabetes, but is not unique to it and can be seen in other diseases as well. Usually, if starchy food is left in the mouth, the sweetness can be felt inside the mouth under the action of salivary amylase. At the same time, if the human digestive system is disordered, the secretion of digestive enzymes in the mouth is abnormal, or if too sweet drinks are taken within a short period of time, the flavoring or sweeteners in the drinks may also remain in the mouth, followed by sweetening. In addition, diabetic patients in the early stage of the disease, due to the increase in blood sugar, the sugar in the mouth increases, and often also feel the performance of sweetness in the mouth. Patients are advised to visit the gastroenterology or endocrinology departments of hospitals to test their blood sugar to clarify whether they are diabetic. If diabetes is diagnosed, the patient needs to actively cooperate with the doctor to control blood sugar, exercise appropriately and take medication on time. Because poor long-term control of blood sugar in diabetes may lead to many serious complications and affect the patient’s quality of life.