Lymphocyte is a kind of immune cell, the reference value of normal adult lymphocyte percentage is 20%-40%, when the absolute value is high the human body’s immunity will be lowered, it is easy to infect some diseases in this period, the cause of high lymphocyte is commonly found in viral infectious diseases, such as influenza. The proportion of lymphocytes in newborn babies is lower than that of neutrophils, and the proportion of lymphocytes increases slowly with age. When the baby is 4-7 days old, the proportion of lymphocytes and neutrophils is basically close to each other, and then the proportion of lymphocytes slowly exceeds the proportion of neutrophils, so the proportion of lymphocytes has always been dominant in the age group of 4-7 days old to 4-7 years old. Between the ages of 4-7 years, the proportion of lymphocytes is somewhat higher than that of neutrophils. As we get older, the lymphocyte ratio slowly decreases, and after 7 years of age, it is close to the normal adult value. Generally speaking, a high lymphocyte ratio may indicate the presence of viral infections, but for infants and children, a high lymphocyte ratio may also be normal, and may not always indicate the presence of a viral infection. It is not possible to rely solely on the results of routine blood tests to determine whether there is a disease state and what kind of disease it is.