【Objective】 To investigate the body mass index(BMI) and the influence factors of infants in Tongling province and to offer reasonable basis for maternal and child health care. 【Method】 The data of their first time physical examination from 1 308 infants aged 3~4 months who had child health care outpatient in our hospital were collected,the BMI and the influence factors of BMI were calculated and analyzed. 【Results】 BMI was significantly different in gender,feeding patterns,birth weight and the level of parents' education(P<0.05),boys' BMI mean was higher than girls';infants who had breast feeding had higher BMI mean than infants who had artificially bred;BMI mean was growing significantly with the increase of birth weight;BMI mean of infants aged 3~4 months of Tongling province was higher than the WHO'S(2006). 【Conclusion】 BMI is influenced by gender,feeding patterns,birth weight and early birth.