Objective To explore the risk factors of birth weight,and to provide a proof for reducing the incidence of low birth weight infants and fetal macrosomia. Methods 642 cases born in Shaanxi Provincial People's Hospital were investigated retrospectively from January to May in 2015.Maternal general,previous reproductive history,living conditions during pregnancy and illness etc were collected.The risk factors of birth weight were analyzed by univariate analysis of variance and multivariate generalized linear regression analysis. Results Univariate analysis showed that the birth weight of low education,a history of spontaneous abortion and induced abortion,exposure to secondhand smoke during pregnancy,pregnancy sickness were lower (P<0.05),while the birth weight of infant whose mother supplement sufficient folic acid in pregnancy was higher (P<0.05).And the birth weight of boy was higher (P<0.05).Multivariate generalized linear regression analysis showed that the birth weight of exposure to secondhand smoke during pregnancy,a history of spontaneous abortion,pregnancy sickness were lower (β=-205.555,β=-210.675,β=-102.709,all P<0.05). Conclusions Birth weight is affected by many factors.Pregnant women should increase awareness of self-care during pregnancy,adopt a healthy lifestyle,strengthen nutrition,regular check-ups,and reduce the incidence of the disease during pregnancy.