The gestational age of preterm babies will be corrected after birth, and the time to start complementary feeding will be 6 months after the original due date, based on the original due date. Normal full-term fetus will start to add complementary food in the sixth month after birth. Due to premature birth, the development of the gastrointestinal tract, respiratory system, cardiovascular system and other systems of preterm infants lags behind that of full-term infants. Preterm babies can reach the state of normal full-term babies through fine care in the later stages. The gestational age of preterm infants needs to be corrected after birth, generally taking the original due date, i.e., 40 weeks of gestational age as the base point, and supplemental food can be added six months after the original due date. The amount of complementary foods added needs to be changed flexibly according to the growth and development status of the preterm infant at that time.