Pelvic fractures with retroperitoneal hematoma are frequent injuries, and there are multiple treatment options for patients. In this case, a 35-year-old female patient suffered an unstable pelvic fracture due to a car crash, accompanied by the formation of a huge retroperitoneal hematoma. The vital signs of patient were not stable. The patient immediately underwent active anti-shock therapies such as multi-channel infusion, blood transfusion, blood volume supplementation, and blood pressure elevation. However, the vital signs of patient remained unstable, the abdominal circumference increased, hemoglobin decreased rapidly, and the plasma protamine paracoagulation (3P) test was positive. So, tracheal intubation and mechanical ventilation were performed. Experts from various departments were invited to form an emergency multidisciplinary team (MDT), and exploratory laparotomy was selected. Intraoperative exploration revealed the formation of a huge retroperitoneal hematoma, and there was no bleeding or abdominal organ rupture.So, five large gauzes were developed and packed into the extra peritoneal space to stanch bleeding. Following successful hemostasis, the pelvic external fixator was positioned. Re-surgery was performed 78 hours after surgery to remove all gauzes. At 2.5 months postoperatively, the pelvic external fixator was also removed.Ultimately, the patient achieved good surgical results. Pelvic gauze packing combined with an external fixator is a rapid and effective treatment strategy for critical and huge retroperitoneal hematomas caused by unstable pelvic fractures. To our knowledge, this has not been previously reported.