Objective To study the microecological status of vaginal flora in pregnant women with preterm premature rupture of membranes (PPROM) and the effect of different anti infection treatment timing on pregnancy outcome, so as to provide reference for improving maternal and infant outcomes. Methods The clinical data of 94 pregnant women with PPROM treated in Gaozhou Maternal and Child Health Hospital from January 2018 to March 2021 were analyzed retrospectively, and they were used as the PPROM group. In addition, the clinical data of 94 pregnant women with normal late pregnancy treated in the same period were selected as the healthy control group. The vaginal flora microecological status and infection situation of the two groups of research objects were analyzed, and the vaginal dominant bacteria of the two groups of research objects were compared, and the differences of white blood cell count, pregnancy outcome, neonatal body mass and length of hospital stay of PPROM pregnant women at different treatment time after membrane rupture [6 h after membrane rupture (the early group) and 18 h after membrane rupture (the late group)] were analyzed and compared. Results The incidence of dysbacteriosis, bacterial vaginosis (BV) and vulvovaginal candidiasis (VVC) in the PPROM group were significantly higher than those in the healthy control group; the proportion of gram-positive cocci, gram-positive bacilli and gram-negative bacilli in the PPROM group was significantly higher than that in the healthy control group, and the proportion of lactobacillus was significantly lower than that in the healthy control group; the proportion of pregnant women with prenatal white blood cell count <10×109 /L in the early group was significantly higher than that in the late group, the proportion of white blood cell count >15×109 /L was significantly lower than that in the late group; the incidence of intrauterine infection and neonatal infection in the early group were significantly lower than those in the late group; the hospitalization time of newborns in the early group was significantly shorter than that in the late group (all P<0.05); there was no significant difference in the incidence of bacterial flora inhibition and neonatal birth weight between the two groups (all P>0.05). Conclusion Pregnant women with PPROM have obvious microecological imbalance of vaginal flora.Early anti-infective treatment 6 hours after membrane rupture can reduce the risk of intrauterine infection, shorten the hospitalization time of newborns, and significantly improve the prognosis of mothers and infants.