The standard for a small amount in infants and young children is a diurnal urine output of less than 400 ml/m2. There are many reasons for children’s oliguria, including physiological oliguria and pathologic oliguria. First of all, physiologic oliguria is mainly caused by too little water intake, because too little water intake, urine production will be relatively less. Secondly, due to pathological factors, if the child suffers from acute enteritis, it will cause diarrhea, resulting in an increase in the number of stools and the amount of defecation, which will also cause oliguria. Children’s oliguria varies greatly from one individual to another, and if the 24-hour urine output of infants and children is <400ml/m2 per square meter of body surface area, it falls into the category of oliguria, and the cause needs to be found in a timely manner.