Preterm infants do not have six major features, features can be divided into appearance features and physiological features. 1. Appearance features: reddish skin, edema, cui-ui hair; head is bigger, about 1/3 of the proportion of the whole body; hair is fine and soft; mammary glands without nodules or nodules <4mm; male infants have not descended or have not descended all the way, female infants labia majora can not cover the labia minora; soles of the feet with less texture. 2. Physiological characteristics (1) Respiratory system: insensitive to hypoxia and hypercapnia; unable to effectively stimulate the respiratory center; shallow, rapid and irregular respiration; prone to periodic respiration. (2) Circulatory system: fast heart rate, low blood pressure, and open ductus arteriosus in some preterm infants. (3) Digestive system: aspiration pneumonia often caused by difficulty in breastfeeding or milk aspiration; delayed expulsion of meconium; necrotizing small bowel colitis may occur; susceptible to kernel jaundice; susceptible to hypoproteinemia, edema, or hypoglycemia. (4) Urinary system: susceptible to hyponatremia, glycosuria, causing late metabolic acidosis. (5) Hematological system: low level of erythropoietin, physiological anemia appears earlier. (6) Nervous system: the younger the gestational age, the more difficult it is to elicit primitive reflexes or incomplete reflexes. (7) Body temperature: preterm infants' sweat glands are poorly developed and their body temperature rises when the ambient temperature is too high; the thermoregulatory center is imperfectly developed and prone to hypothermia and even scleroderma. Preterm babies and full-term babies may be relatively delayed in all aspects of development, should consult a doctor in a timely manner, under the care and treatment of a professional doctor so that preterm babies grow better.