Many diseases can be complicated by fever in clinical practice, so the differential diagnosis of fever is difficult. The differentiation in clinical practice is based on the temperature of the patient at the time of fever, whether the fever has a corresponding regularity, and the other corresponding clinical symptoms that accompany it. There are two major clinical causes of fever, one is infectious and the other is non-infectious. Infectious fever is mainly caused by microbial infections, including bacteria, viruses, mycoplasma, chlamydia, spirochetes and parasites, and can be caused by infections of the respiratory system, digestive system, urinary system and skin. In addition, non-infectious diseases such as rheumatic fever, rheumatoid, rheumatoid arthritis, systemic lupus erythematosus or polymyositis, as well as malignant tumors such as lymphoma, bone tumors, and blood diseases such as leukemia can also cause fever. Therefore, when fever occurs, especially if the fever is recurrent, it is recommended to seek timely medical attention, identify it through necessary tests, and finally confirm the diagnosis and provide timely treatment.