Objective To investigate maternal antenatal ambroxol hydrochloride incidence of neonatal respiratory distress syndrome affected. Methods Since our hospital between October 2012-2014 October has admitted 248 cases of pregnant women with preterm labor signs as research subjects, according to the gestational age of the case will be divided into two groups, Group A pregnant woman's gestational age ≤35 weeks Group B pregnant gestation> 35 weeks, patients were randomly divided into two groups in turn, that the patients in the control group A-, A-observation group; B-B-observation group and control group, respectively, to its line of conventional drugs for pregnant women in the control group treatment, observation group were treated with ambroxol hydrochloride for treatment, compared to four groups of neonatal respiratory distress happen. Results A-control group incidence of neonatal distress (18) 29.03%, B-group the data (25) 40.32%; A-observation group incidence of neonatal respiratory distress (8) 12.90%, B-The data for the observation group (14) 22.58%, comparing two sets of data were statistically significant difference, P<0.05. Conclusion gestational age <35 weeks is ambroxol hydrochloride prenatal prevention of neonatal respiratory distress best time.