The causes of postpartum hemorrhage are as follows: 1, weak uterine contractions: tension and anxiety, large fetus, history of previous surgery, poor uterine contraction before delivery of the fetus, resulting in postpartum hemorrhage. In addition, excessive use of sedatives, anesthetics and uterine contraction inhibiting drugs before delivery can also lead to postpartum hemorrhage; 2, placental factors: including placental implantation, placental adhesions, such as a history of multiple previous miscarriages, a history of uterine surgery, which can easily lead to placental implantation in this pregnancy and cause postpartum hemorrhage; 3, soft birth canal laceration: vaginal assisted delivery procedures, such as forceps assisted delivery and lead to bleeding; 4, abnormal coagulation function: primary and secondary coagulation abnormalities, resulting in postpartum hemorrhage. The above four factors complement each other and develop one after another, and do not exist independently.