Elderly people always have fever in the afternoon, which may be related to upper respiratory tract infections, tuberculosis, malignant tumors, and connective tissue diseases. 1. Upper respiratory tract infections: most often seen in viral infections, due to the virus invades the human body, will be in the body of a large number of replication and reproduction, the clinic will be prone to recurring fever phenomenon. Especially the elderly are weaker and vulnerable to viruses. Because the virus is difficult to be removed, so it is also easy to appear repeatedly in the afternoon fever. 2. Tuberculosis: it is a kind of lung disease caused by the infection of tuberculosis bacillus, which is mainly manifested in the clinic as low fever in the afternoon, and may be accompanied by cough, hemoptysis and emaciation. 3. Malignant tumor: due to the tumor cells will cause invasion of the surrounding tissues, affecting the physiological function of normal tissues, and prolonged morbidity will lead to malignant disease, which will be manifested as recurrent fever in the clinic, accompanied by lethargy and fatigue phenomenon. 4. Connective tissue disease: mainly including systemic lupus erythematosus, dry syndrome, etc., due to autoimmune system abnormalities, patients are prone to recurrent fever, rash or joint abnormalities. Because of the many causative factors, the specific situation needs to be analyzed in conjunction with other clinical manifestations and treated under the guidance of the doctor.