Lymphocyte increase is mainly caused by the following factors: First, physiological factors: during the developmental period of children, after 4-6 days to the age of 4-6 years, lymphocytes will mostly appear physiological increase, which is normal. Second, infectious diseases: mainly viral infections, such as measles, rubella, chickenpox, mumps, infectious mononucleosis, hepatitis, as well as whooping cough, Mycobacterium tuberculosis infection, Brucella infection, etc., may lead to lymphocytosis. Third, neoplastic diseases: such as acute and chronic lymphocytic leukemia and lymphoma. Fourth, other factors: the recovery period of infectious diseases, and the rejection of some grafts. When aplastic anemia, granulocytopenia or granulocyte deficiency occurs, neutrophils will mostly be relatively reduced and lymphocytes will be relatively increased, but the absolute value of lymphocytes is not increased, which may be related to the primary disease.