To Evaluate the Efficacy and Safety of Genalumab for Injection in the Treatment of Active Systemic Juvenile Idiopathic Arthritis.

• Male and female patients, with the remaining before age 2 years old or more and \& lt; 18 years old;
• 2001 ILAR classification criteria for the diagnosis of confirmed sJIA 2 or more months: onset age must \& lt; At 16 years of age, symptoms included: ≥1 case of arthritis, accompanied by or prior to ≥2 weeks of recurrent fever, including remittenor fever for ≥3 consecutive days (maximum daily body temperature ≥39 ° C, body temperature falling below 37 ° C between 2 heat peaks), accompanied by at least one of the following symptoms: ① a transient, non-fixed erythematous rash; ② systemic lymph node enlargement; Swelling of the liver and/or spleen; ④ Serositis.
• Agree to use effective means of contraception throughout the study period and for 6 months after the end of treatment.

Exclusion Criteria:

• Pregnant or lactating female subjects
• A history of allergic reactions to investigational drugs or to molecules with similar structures; Those who cannot be given intramuscular injections；
• History of pericarditis, myocarditis, serositis, bacterial heart valve or endocarditis within 6 months before screening; Patients who had been diagnosed with MAS within 6 months prior to screening, or had relevant symptoms and signs at screening, and were suspected of having MAS as assessed by the investigators；
• There are other rheumatic diseases such as Kawasaki disease, polyarteritis nodosa and so on. History of autoinflammatory diseases such as familial Mediterranean fever, high IgD syndrome, NLRP3-related autoinflammatory diseases；
• Patients with a history of interstitial lung disease, pulmonary fibrosis, alveolar proteinosis, or pulmonary hypertension; Patients with a history of repeated invasive fungal infection; In the 7 days prior to randomization, there were infections that required control with systemic antigenic microbiotics (including antibacterial, antiviral, antifungal, etc.)；
• Subjects with a history of TB exposure or suspected TB symptoms.