Abstract: Objective To explore the high-risk factors of severe maternal perineal tears by analyzing the clinical data of 27 cases. Methods The case group enrolled 27 cases of severe maternal perineal tear after a vaginal delivery in Anhui Maternal and Child Health Hospital from February 2016 to April 2019. A total of 54 pregnant women who has adjacent hospitalization number as a control group according to 1∶2 ratio. The clinical data of case and control group were compared by two-sample t-test, χ² test and binary logistic regression. Results The incidence of severe perineal tears was 27/28 334(95.29/100 000). The Bleeding volume after delivery and incidence of postpartum urinary retention in study group was higher than that in the control group(P<0.05), the severe maternal perineal tear in study group were repaired immediately, and guided defecation, used antibiotic after surgery. The long-term prognosis of them are good. The single factor analysis showed that there were statistically significant differences in Maternal BMI(OR=7.552, 95% CI: 2.136 to 26.696) and neonatal weight(OR=20.511, 95% CI: 4.552 to 92.421) between the two groups(P<0.05). There was no statistically significant difference in age, forceps delivery, episiotomy, labor analgesia, midwife's seniority and delivery period between the two groups(all P>0.05). Conclusion High maternal BMI and neonatal weight are the high-risk factors of severe maternal perineal tears. Pregnant women increase their weight reasonably and control neonatal weight has a positive effect on reducing the occurrence of severe perineal tears.