Jaundice is caused by high levels of free bilirubin in the blood that exceed the body’s metabolic capacity, resulting in yellow urine, yellow sclera and yellow skin. Jaundice is common in newborns with physiological or pathological jaundice, liver disease, bile duct obstruction, and other conditions that increase bilirubin production, impair metabolism, and impede excretion. The normal adult total bilirubin level is usually within 17.1 μmol/L, including 3.42 μmol/L of conjugated bilirubin and 13.68 μmol/L of unconjugated bilirubin. When the bilirubin is between 17.1 and 34.2 μmol/L, it is not easily detected clinically and is called occult jaundice. While the bilirubin level in the body exceeds 34.2 μmol/L, it is called dominant jaundice, and yellow staining of the skin and sclera is easily detected. Because of environmental changes in newborns, the change from an oxygen-deficient environment in the body to an adequate supply of oxygen from the outside world leads to the destruction of too many red blood cells in the body and the breakdown and metabolism of hemoglobin to form bilirubin excreted into the liver and blood, together with the limited metabolic function of the liver in newborns, physiological jaundice occurs in most newborns after birth. Physiological jaundice in newborns generally begins to appear 2-3 days after birth, peaks in 4-5 days, begins to subside in about a week, and generally subsides completely within three weeks. The normal range of bilirubin level is different for different days of age and for different situations such as prematurity. The bilirubin level of physiological jaundice in newborns is generally within 225 mmol/l, and if it exceeds 225 mmol/l then attention should be paid to the examination to exclude pathological jaundice and active blue light treatment to prevent the occurrence of bilirubin encephalopathy. In conclusion, the reference range of bilirubin level is different in different age groups, and when the bilirubin level exceeds the normal range for that age group, we should actively check to exclude hepatobiliary diseases, and when newborns develop hyperbilirubinemia and bilirubin level exceeds the safe range, we should not only actively check to exclude pathological jaundice, but also actively carry out blue light irradiation to control the continued increase of bilirubin level as soon as possible to prevent the occurrence of nuclear jaundice.