This study is a multicenter, randomized, double-blind, parallel-group, placebo-controlled Phase III clinical trial designed to evaluate the efficacy and safety of TQC2731 injection (420 mg Q4W) in adult subjects with inadequately controlled severe asthma. A total of 660 subjects are expected to be enrolled, with subjects randomized in a 1:1 ratio to receive either TQC2731 (420 mg Q4W) or placebo (Q4W) via subcutaneous (SC) administration.

Inclusion Criteria:

• Sign the informed consent form before the trial to fully understand the purpose, process and possible adverse reactions of the trial;
• Age 18 ~ 75 years old, gender is not limited;
• Documented physician diagnosis of asthma at least 12 months prior to Visit 1;
• Subjects who received high-dose Inhaled Corticosteroids (ICS) in asthma control medications prescribed by their physicians at least 6 months prior to Visit 1;
• There must be a record of receiving a stable total daily dose of ICS at least 3 months prior to visit 1;
• There must be a record of the use of other asthma control medications at a stable dose at least 3 months prior to visit 1; For subjects taking maintenance oral hormones, the dose of oral hormones is up to 10mg prednisone per day or 20mg every other day (or equivalent) and must be stable for at least 30 days prior to visit 1 and during treatment.
• Documented at least 2 asthma exacerbations in the 12 months prior to Visit 1 and no major asthma exacerbation events in the 1 month prior to signing informed.

Exclusion Criteria:

• Have a clinically significant lung disease other than asthma；
• Pre-existing autoimmune disease;
• A history of known or suspected immunosuppression, including a history of invasive opportunistic infections;
• Any disease that has not been determined to be stable by the investigator；
• Cancer history: Patients with basal cell carcinoma, skin localized squamous cell carcinoma, or cervical carcinoma in situ are eligible to be enrolled in this study if they had completed curative therapy for at least 12 months prior to visit 1. Patients with other malignancies who had completed curative treatment for at least 5 years prior to visit 1 could be enrolled in the study.
• Current smoker or smoking history ≥10 pack-years (former smokers with smoking history <10 pack-years had quit smoking less than 6 months before interview 1);
• Other factors determined by the investigator that subjects were not suitable to participate in the study.