The causes of low-grade fever are complex and are commonly associated with Mycoplasma pneumoniae, Chlamydia, and Mycobacterium tuberculosis infections, as well as rheumatic immune and tumor patients. For the treatment of low fever, the first thing is to clarify the diagnosis and not to apply antipyretic drugs blindly. Many patients in the clinic go to the hospital only because the long-term application of antipyretic drugs does not work well, and then delay the diagnosis and the best treatment period. There are various causes of prolonged hypothermia. If the patient has a history of respiratory tract infection, such as common sore throat, cough, low fever, headache, etc., routine blood tests and Chlamydia pneumoniae tests are required. There are also patients with blood disorders, such as chronic granulocytic leukemia, where, in addition to low-grade fever, the patient will also have symptoms such as malaise, excessive sweating, weight loss and wasting. Patients with anemia and some women with physiological periods (dysmenorrhea) can develop hypothermia. Therefore, the diseases involved in hypothermia are very complex and there is a wide range of diseases. Patients with prolonged hypothermia must be taken seriously enough. In addition to routine blood tests, C-reactive protein, Mycoplasma pneumoniae and Chlamydia, patients are advised to check for rheumatic immunity, infectious diseases and tumors. Unexplained hypothermia should not be abused to reduce fever, so as not to delay diagnosis and treatment.