Very low urinary sodium excretion is a significant clinical manifestation of hyponatremia. The normal value of blood sodium is 142 mmol/L (135-145 mmol/L), and blood sodium below 135 mmol/L is considered hyponatremia. Urinary sodium: normal adult 70-90 mmol/24h, about 4,1-5,3g of sodium chloride. if urinary Na+. Sodium in human body mainly exists in extracellular fluid. The daily sodium requirement is 1~2mmol/kg for full-term newborns and 3~4mmol/kg or higher for premature babies. Because of the low ability of the kidneys to regulate water, electrolytes and acid-base balance in newborns, especially in preterm infants, edema and hyponatremia are likely to occur when excessive water intake occurs. Therefore, excessive water intake should be controlled in preterm infants. Prevention of hyponatremia should start from pregnancy health care: 1. The use of diuretics or low salt diet for maternal hypertension can affect the newborn to cause hyponatremia; 2. After birth, we should actively prevent and control abnormal gastrointestinal tract loss such as diarrhea; 3. We should prevent and control asphyxia, ischemic and hypoxic encephalopathy, cerebral hemorrhage and other disorders; 4. We should prevent and control renal disorders to avoid renal drainage disorders, low response to aldosterone, renal dysfunction, etc.; 5. Medical or improper feeding caused by excessive water intake and low sodium intake resulting in hyponatremia. Sodium in human body mainly exists in extracellular fluid, and the daily sodium requirement is 1~2mmol/kg for full-term newborns and 3~4mmol/kg or higher for preterm babies, and the ability of kidneys to regulate water, electrolyte and acid-base balance is low in newborns, especially preterm babies, so edema and hyponatremia easily occur when excessive water intake. The prevention of hyponatremia should start from the health care during pregnancy. The use of diuretics or low-salt diet in pregnant mothers with hypertension can affect the neonate to cause hyponatremia; after birth, we should actively prevent and control abnormal gastrointestinal tract loss such as diarrhea; prevent and control asphyxia, ischemia, hypoxic encephalopathy, cerebral hemorrhage and other disorders; prevent and control renal disorders to avoid kidney drainage disorders, low response to aldosterone, renal dysfunction, etc.; moreover, we should prevent medical origin or improper feeding It is also necessary to prevent hyponatremia caused by excessive water intake and low sodium intake due to improper feeding.