Childhood-onset thrombotic thrombocytopenic purpura (TTP) is very rare, and this article summarizes the clinical data of a child with immune-mediated TTP (iTTP) that occurred 4 years after diagnosis of systemic lupus erythematosus (SLE). The patient was initially diagnosed with SLE and lupus nephritis (Ⅳ+Ⅴ) at the age of 2 years after presenting with edema, hematuria, and albuminuria, and went into remission after treatment with glucocorticoids and tacrolimus, which was discontinued at 5 years old. And one year later, the child was admitted to the hospital with a sudden onset of cutaneous hemorrhagic spots, fatigue, and poor appetite. Laboratory examinations after admission were as follows. Urine protein was "++~+++", and urine red blood cell count was 78.1 per high-power field, with uniform red blood cell morphology. Hemoglobin was 85g/L, mean corpuscular volume of red blood cells was 80.5 fL, platelets were 7×10⁹/L, erythrocyte fragmentation were positive, lactate dehydrogenase was 998 U/L, creatinine was 34.2μmol/L, and indirect bilirubin was 23.1μmol/L. Anti-nuclear antibody in homogeneous type was >1:1000, anti-double-stranded DNA was >300 IU/mL, anti-U1 ribonucleic acid protein antibody was "++", anti-nucleosome antibody was "+", anti-ribosomal P protein antibody was "+", complement C3 was 0.15 g/L, and complement C4 was 0.05 g/L. The activity of plasma ADAMTS13 was 0.72%, and the plasma ADAMTS13 inhibitor was positive. The direct antiglobulin test was positive, the erythrocyte sedimentation rate was 44mm/h, and the PLASMIC score was 7 points. Combined with the history, clinical manifestations and laboratory findings, the child was definitively diagnosed with SLE associated iTTP. After two administrations with eculizumab combined with glucocorticoids, plasma infusion, immunoglobulin, and hydroxychloroquine sulfate, the child’s platelets quickly returned to normal, plasma ADAMTS13 activity rebounded to 12%, and plasma ADAMTS13 inhibitor turned negative. There are no domestic case reports of iTTP in children treated with eculizumab, and the results of our case suggests that complement inhibitors are effective in controlling iTTP disease activity.