Angiosarcoma is a rare subtype of soft tissue sarcoma with identifiable vascular differentiation. It can occur at any age and develop throughout the body, but it is most commonly found in skin, soft, and breast tissues. Primary retroperitoneal angiosarcoma is rarely reported in the relevant literature. This article reports a case of primary retroperitoneal angiosarcoma in a middle-aged man, with the relevant literature reviewed in detail. A 46-year-old male had experienced left waist pain for 2 months. An ultrasonic examination revealed a mass in the left retroperitoneum, and left retroperitoneal lesions were confirmed via computed tomography (CT) and magnetic resonance imaging (MRI). The tumor was removed surgically, and the CT scan revealed local tumor recurrence after 1 month when the first adjuvant therapy was performed. The patient died of a massive hemorrhage from a ruptured tumor. Angiosarcoma has high malignancy and a poor prognosis. Its early diagnosis and treatment significantly impact the long-term survival rate of patients.