There are four main causes of postpartum hemorrhage: one is uterine atony, two is due to trauma in the soft birth canal, three is due to placental factors, and four is coagulation dysfunction. Uterine atony is the most common cause of postpartum hemorrhage clinically. Various factors can lead to uterine atony, such as maternal exhaustion during labor due to not eating, leading to physical decay, which can also cause uterine atony. Additionally, an excessively large uterus, such as from excessive amniotic fluid, twins, or triplets, can lead to poor uterine contraction and retraction rates after childbirth. As for injuries in the soft birth canal, they mainly occur due to insufficient protection of the perineum during childbirth or inappropriate use of vacuum assistance during the second stage of labor, causing trauma in the soft birth canal. Placental factors include placental adhesion, placenta accreta, partial placental abruption, and retained placenta, all of which can lead to postpartum bleeding due to placental issues.