If you have a fever that does not go away, you need to take a detailed medical history first. Fever is divided into infectious fever and non-infectious fever. Infectious fever has a more rapid onset and lasts for a shorter period of time. If a patient suddenly develops a high fever, infectious fever is more likely to be considered, and it is necessary to ask specific questions about the accompanying symptoms. If the patient has coughing, coughing, chest pain, shortness of breath and other symptoms, it is necessary to consider lung disease, and it is recommended to do lung CT, chest X-ray and other examinations. If accompanied by frequent urination, urgent urination and painful urination, urinary system infection needs to be considered. If there is nausea, vomiting, abdominal pain and diarrhea, gastrointestinal infection needs to be considered. If the patient is having low fever in the afternoon with night sweats and wasting for a longer period of time, tuberculosis needs to be considered. Tuberculosis is sometimes difficult to diagnose and needs to be combined with the patient’s symptoms and relevant auxiliary examinations to make a clear diagnosis. For example, tuberculosis antibody, sputum test for tuberculosis bacteria, and T-SPOT test can be done. If the cause of infectious fever is unclear, non-infectious diseases such as rheumatic immune system diseases, hematological system diseases and malignant tumors need to be considered. If the cause of a long-standing fever is not identified, bone aspiration is needed to rule out hematologic diseases. For women with recurrent fever, consider the possibility of rheumatic immune system diseases. In elderly patients, it is also important to pay attention to the possibility of tumor fever.