To investigate the changes of vaginal flora and inflammatory factors of women with premature rupture of fetal membranes (PROM) during the third trimester pregnancy, and to analyze its influence on their pregnancy outcomes. Methods: During the third trimester pregnancy, 180 pregnant women with PROM were enrolled into observation group and 100 normal pregnant women were enrolled into control group. The distributions of vaginal flora of the women ante partum in the two groups were measured, and the levels of serum highly sensitive C-reactive protein (hs-CRP), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) of these women were also detected. The situations of vaginal flora and inflammatory factors of women were compared between the two groups, and the relationship between the levels of vaginal flora and inflammatory factors of women and their pregnancy outcomes were analyzed. Results: The proportion of lactobacilli of women in the observation group was significant lower than that of women in the control group, but the proportion of gram-positive bacilli, gramnegative bacilli, or grampositive cocci of women in the observation group was significant higher (P<0.05). The detection rate of various pathogens (staphylococcus haemolyticus, enterococcus faecalis, enterococcus cloacae, or proteus, etc.) of women in the observation group was significant higher than that of women in the control group (P<0.05).  The mean value of vaginal pH of women in the observation group was 7.15±0.43, which was significant higher than that (4.82±0.36) of women in the control group (P<0.05). The proportions of vagina density grade Ⅱ and Ⅲ, vagina flora diversity grade Ⅱ and Ⅲ, and vagina microecology of women in the observation group were significant lower of those of women in the control group (all P<0.05). The serum level of IL-6 of women in the observation group was significant higher than that of women in the control group (P<0.05), but the levels of hs-CRP and TNF-αof women had no significant diffrent between the two groups (P>0.05). In the observation group, the incidences of premature delivery, neonatal infection, neonatal pathological jaundice, and puerperal infection of women with endovaginal microecologics dysbiosis were significant higher than those of women with normal endovaginal microecologics (P<0.05), but the incidence of low birth weight infants, the level of serum IL-6 of women with normal pregnancy outcomes was significant lower than that of women with adverse pregnancy outcomes (P<0.05), and the levels of serum hs CRP and TNF-αhad no significant different (P>0.05). Conclusion: The vaginal PH increased, lactobacilli decreased, and inflammatory reaction of pregnant women during the third trimester of pregnancy may be the main factors of PROM. The imbalance of vaginal flora and inflammatory reaction may also increase the risk of adverse maternal and infant outcomes, such as premature delivery, puerperal infection, fetal distress, and neonatal infection.