Physiological weight loss in newborns does not exceed 10% of the newborn’s birth weight. The cause of physiological weight loss in newborns is caused by insufficient milk intake after birth, faster evaporation of water in newborns, and improper hydration of newborns, which can cause physiological weight loss in newborns, and defecation in newborns, thus aggravating the physiological weight loss in newborns. The physiological causes of weight loss in newborns are normal, the child’s mental state is better and so is the milk eating, but if the physiological weight loss in newborns is more than 10% of their body weight, the cause should be found in time, some newborns are not physiological weight loss, which is mainly due to the parents of the newborn, giving the newborn adequate supplemental milk powder.