Differential diagnosis of the cause of fever to be investigated mainly consider the following aspects: 1, infectious diseases account for 40% -50% of the cause of fever to be investigated, a wide range of pathogenic bacteria, including bacteria, fungi, viruses, rickettsiae, chlamydia, mycoplasma, as well as protozoa and helminths, etc., all of which can cause fever, and the most common bacterial diseases and viral diseases; 2, oncological diseases, accounting for about 20% of the causes of fever to be investigated, and the most common lymphoma. Fever is caused by the solid tumor itself necrosis, hemorrhage to produce tumor antigen or pyrogen, causing fever, with lymphoma being the most common; 3, connective tissue diseases and vascular diseases, accounting for 20%-30% of the causes of fever to be investigated, such as systemic lupus erythematosus, rheumatic fever, rheumatoid arthritis, adult Still syndrome, dermatomyositis, scleroderma, vasculitis and so on, all of them are manifested by fever as the main manifestation, and the laboratory examination can The laboratory examination can find elevated immunoglobulin, positive autoantibodies such as antinuclear antibody, antimitochondrial antibody, rheumatoid factor, etc.; 4. Other kinds of fever account for about 10% of the fever, including drug fever, tissue injury, endocrine diseases. Drug fever is drug-induced allergic vasculitis, often associated with allergy, rash, arthralgia, blood eosinophilia, occurring after 7-10 days of medication, manifested as a drop in body temperature and then rise again, stopping the drug for 2-3 days can be self-reduction of fever. Tissue damage such as myocardial infarction, cerebral infarction, pulmonary infarction, etc., endocrine system diseases such as hyperthyroidism, also often accompanied by fever.