It's of great importance to effectively induce and maintain disease remission in patients with moderate to severe ulcerative colitis (UC). Vedolizumab (VDZ) is known for its high safety profile and confirmed therapeutic efficacy in UC treatment. However, according to the experience in clinical practice, the effect onset speed of vedolizumab is relatively slow. Upadacitinib (UPA), however, works quickly, which complements the defect of slow onset of VDZ induction. However, the safety of UPA used in situations such as infection and tumors is inferior to that of VDZ, and long-term use requires testing for the risk of adverse events such as deep vein thrombosis. Therefore, if the advantages of long-term maintenance therapy safety of VDZ and rapid induced remission of UPA are fully utilized, the combination of VDZ and UPA induction for 8 weeks, followed by the use of single drug VDZ in maintenance therapy, can maximize the clinical benefits of UC patients. Due to the lack of high-level clinical research data at home and abroad, we plan to conduct a multicenter prospective randomized controlled clinical study to provide the evidence-based basis for the efficacy analysis of the sequential treatment of moderate to severe UC patients with VDZ and UPA.