Erythrodermic psoriasis (EP) is a rare and severe type of psoriasis. Common systemic therapies for children with EP include treatment with glucocorticoids, cyclosporine, acitretin, and methotrexate. Although these drugs are effective, they may cause serious side effects to children. Secukinumab has recently demonstrated efficacy in treating plaque psoriasis, but its efficacy in EP children remains unknown. We report a case of a seven-year-old patient who transitioned from generalized pustular psoriasis (GPP) to EP after routine systemic drug treatment. The patient was then treated with secukinumab. The patient’s condition improved noticeably within 48 hours after the first injection. After the fifth injection, she almost completely cleared her skin lesions and achieved Psoriasis Area and Severity Index 90 (PASI 90) scores. During this period, she experienced only one respiratory infection. She completed all 11 doses of secukinumab by October 14, 2022, with no new rash (PASI 100) and no adverse drug reactions. Follow-up observation on March 15, 2023, showed no new rash (PASI 100) and no adverse reactions after medication withdrawal. This case suggests that it may also be effective in treating children with EP.