Prolonged low fever, especially if the fever symptoms are not effectively relieved after the application of antipyretic drugs, must be taken seriously enough. In addition to considering some common respiratory infectious diseases, rheumatic immune and hematological diseases as well as some infectious diseases and even tumors should also be considered. The causes of prolonged low-grade fever are complex and varied. The most common cause is Mycobacterium tuberculosis infection, commonly known as pulmonary tuberculosis, tuberculous pleurisy, and intestinal tuberculosis. The main clinical manifestations of tuberculosis are coughing, coughing up sputum, even coughing up blood, and low fever in the afternoon, accompanied by weakness and night sweats. In this case, you can go to the hospital for routine examinations, such as chest CT examination and tuberculin test. Hypothermia is also common in patients with functional hypothermia as well as in patients with large burns. In addition to this, some infectious diseases, such as AIDS and hepatitis B, should be considered, and patients may also have prolonged hypothermia. There are also non-infectious diseases such as hyperthyroidism, cirrhosis, rheumatic fever, systemic lupus erythematosus, physiological dysmenorrhea, and tumors. In conclusion, patients who develop hypothermia must pay enough attention to it. Persistent low fever should be promptly seen by a hospital. In addition to routine blood, urine, stool, sedimentation, C-reactive protein, mycoplasma pneumoniae, and chlamydia tests, patients are advised to check again for tuberculosis, rheumatic immunity, tumors, and infectious diseases (such as AIDS, hepatitis, gonorrhea, etc.). Until the cause is identified, remember not to use fever-reducing drugs blindly.