Objective To analyze the relationship between the early growth stage body mass index (BMI) increasing span and the childhood growth overweight or obesity in low birth weight infants,and to provide scientific basis for the moderate catch-up growth of low birth weight infants. Methods Children born from October 2011 to September 2012 in Wenzhou were selected retrospectively,and were divided into low birth weight group and normal birth weight group.The weight and length datas of two groups of children at the age of one month,1 year old and 5 years old were collected,then BMI in each stage was calculate respectively.BMI distribution interval was divided according to the BMI boundary value point which from《Standards for growth and development of preschool children》of WHO,and BMI increasing span from one month to one year old was got and then analyse the overweight or obesity probability when they were 5 years old with different BMI increasing span. Results In low birth weight group infants whose BMI increases over 3 or more spans was nearly 25% higher than normal birth weight group.There was no significant difference in the incidence of overweight or obesity between the BMI 0 span or 1~2 span in the low birth weight group,but there were differences between the normal weight group in each BMI increasing span.A certain correlation was found between BMI growth span and growth level in low birth weight infants,all one-month to one-year-old infants' body weight,height,and BMI did not reach the median of WHO which that there BMI were in the same interval.Body weight and BMI were higher than WHO reference medians and also had differences when BMI increased to 5 or more spans. Conclusions Compared with normal birth weight infants,more low birth weight infants have a larger increase range of BMI during the critical growth period,BMI growth span in 1~2 intervals is more favorable for controlling growth and overweight or obesity in the future.