The patient was a girl aged 10 years and 10 months, with weakness, pale complexion, and rash as the initial presentation. She had the manifestations of anemia, thrombocytopenia, hematuria-proteinuria with renal insufficiency, hypocomplementemia, polyserositis, and positive anti-nuclear antibody and anti-dsDNA antibody. The girl was initially diagnosed with systemic lupus erythematosus and lupus nephritis. She demonstrated a suboptimal response to methylprednisolone pulse therapy, intravenous immunoglobulin administration, and therapeutic plasma exchange. She had persistent anemia, thrombocytopenia, abnormal renal function, elevated lactate dehydrogenase, decreased complement factors H and I, increased antibodies to C3 converting enzyme, and normal ADAMTS13 activity. She was diagnosed with complement-mediated hemolytic thrombotic microangiopathy secondary to systemic lupus erythematosus. The patient's condition improved after treatment with two doses of eculizumab (600 mg per dose). Patients with systemic lupus erythematosus complicated by thrombotic microangiopathy often have a severe disease course and poor prognosis; therefore, early recognition and aggressive intervention are crucial for improving outcomes.