Hemophilia is a set of hereditary hemorrhagic disorders of coagulation-dysfunction that can cause repeated bleeding in various tissues and organs. And the patient can be disabled due to bleeding from bones, joints, and soft tissue, or die due to splenic rupture or intracranial bleeding. So it is crucial to detect the site of bleeding in hemophilia patients quickly. Spontaneous spinal canal hematoma is a rare complication of hemophilia, with less than 50 cases reported to date. It can be easily missed and cause serious harm to patients. Hematoma, if untreated, causes irreversible nerve damage by compression of the spinal cord. Early recognition and treatment are most useful to prevent spontaneous spinal canal hematoma. We describe the case of a 21-year-old man with severe lumbago for two days, who had hemophilia A for a decade. The patient was diagnosed with spinal subdural hematoma by magnetic resonance imaging (MRI) after ruling out other causes of lumbago and treated with drugs by a neurologist. The hematoma showed absorption by MRI after six months. In conclusion, spontaneous spinal canal hematoma is a severe complication of hemophilia, which is often missed. This successful case confirms the importance of early diagnosis and treatment of spontaneous spinal canal hematoma. We hope to increase the clinicians' vigilance of this disease.