Normally, a four-and-a-half month old baby weighs between 6.9-8.6kg, but there is variability in the weight of each baby. Four and a half month baby weight between 6.9-8.6kg is usually normal, but the baby’s weight is affected by congenital factors as well as acquired factors, each baby has variability, do not be too demanding to achieve a certain amount of weight. If the baby’s weight is within the normal range, it is normal. Some babies’ weight may fluctuate a little relative to the standard, but their diet, sleep and spirit are all good, which is generally normal. If four and a half months baby’s weight and the same age baby obvious difference, should be timely consultation, in the doctor’s help to clarify the cause of the disease, and then targeted treatment.