Objective:To analyze the clinical data of children with active lupus nephritis(LN) with poor first-line treatment and further treatment with belimumab, and explore the efficacy and safety of belimumab in the treatment of children with LN, so as to provide experience and guidance for clinical treatment of children with LN.Methods:From August 2020 to September 2021, 12 children with LN whose systemic lupus erythematosus disease activity index(SLEDAI)score was ≥8 and with poor first-line treatment were collected, and their clinical manifestations, treatment process, SLEDAI score, complement C3, complement C4, anti-dsDNA antibody titer, and proteinuria relief were analyzed retrospectively.Results:Before treatment with belimumab, the SLEDAI score was 8 in 3 cases, 10 in 5 cases, 12 in 2 cases and 16 in 2 cases.Theurine protein was positive in 6 cases.The anti-dsDNA antibody titer was higher than normal value in 8 cases.The complement C3 decreased in 8 cases and the complement C4 decreased in 6 cases.The SLEDAI scores and the anti-dsDNA antibody of 12 children and 24-hour urine protein quantification of 6 children with positive urine protein began to decrease within 4 weeks after treatment with belimumab.Anti-dsDNA antibody decreased to normal in 12th week and 24 h urine protein decreased to normal in 16th week.The levels of complement C3 and C4 began to rise within 4 weeks, complement C3 returned to normal within 24 weeks, and complement C4 returned to normal within 28 weeks.Conclusion:For LN children with poor response to first-line therapy or persistent disease activity, the addition of belimumab resulted in increased complement, decreased disease activity index and anti-dsDNA antibody titer, and effective relief of proteinuria.The application of belimumab has a certain effect on active LN children with poor response to first-line therapy, which is worthy of clinical promotion.