This article reports a case of an elderly male patient presenting with nephrotic syndrome. Renal biopsy pathology indicated membranous nephropathy, with both renal tissue staining for M-type phospholipase A2 receptor (PLA2R) and serum anti-PLA2R antibodies being negative. Nephrotic syndrome achieved remission following treatment with prednisone combined with tacrolimus; however, the patient relapsed during tacrolimus maintenance therapy. Subsequent laboratory evaluation revealed positive anti-nuclear antibodies and anti-double-stranded DNA antibodies, accompanied by decreased complement levels. Exostosin 1 and Exostosin 2 staining performed on the initial renal biopsy specimen yielded positive results, leading to a diagnosis of lupus nephritis. Due to the patient's history of rituximab-related allergic reactions, pulmonary infection, and acute kidney injury, the subsequent treatment regimen consisted of obinutuzumab sequentially combined with belimumab, in addition to prednisone 10 mg/d. During the two-year follow-up period, the patient's anti-double-stranded DNA antibodies converted to negative, complement levels normalized, proteinuria achieved complete remission, and no adverse events such as severe infection occurred. This article reviews the diagnosis, treatment, and relevant literature for this case, aiming to provide clinical insights for the early diagnosis and selection of therapeutic strategies for similar patients.