Comparative Effectiveness of Upadacitinib vs Corticosteroids as First-Line Therapy for Acute Severe Ulcerative Colitis（UPFRONT）

The goal of this clinical trial is to learn comparative effectiveness and safety of Upadacitinib vs Corticosteroids as First-Line Therapy for Acute Severe Ulcerative Colitis. The main questions it aims to answer are: 1. Whether upadacitinib can effectively induce remission in acute severe ulcerative colitis with an efficacy non-inferior to that of corticosteroids. 2. What adverse reactions may occur with upadacitinib in the treatment of acute severe ulcerative colitis? Researchers will compare upadacitinib with corticosteroids to evaluate the efficacy of upadacitinib in the treatment of acute severe ulcerative colitis.Participants will: 1. Upadacitinib group: Upadacitinib extended-release tablets 45 mg once daily for 8 weeks, then adjusted to 30 mg once daily. 2. Corticosteroid group: Methylprednisolone for injection 60 mg/day. If clinical response is achieved, switch to oral prednisone acetate tablets after 5 days (calculated at 0.75 mg/kg/day), followed by a weekly prednisone taper of 5 mg. When the dose is reduced to 20 mg, taper by 2.5 mg weekly until discontinued, with mesalazine 4 g/day as maintenance therapy. 3. Take drug Upadacitinib or Corticosteroid every day for 3 months 4. Visit the clinic once every 2 weeks for checkups and tests 5. Record the patient's bowel movements and the presence of symptoms such as abdominal pain, while performing colonoscopy, ultrasound examination, and blood tests at the specified time points.