The first-line treatment strategy of moderate to severe UC was a important question at issue. The biological agents had potentiality to alter the disease course of UC. The AGA clinical guidelines had conditional recommend that IFX and other biological agene migtht be first-line therapy for high-risk UC patints but only had low grade evidence.We launched this multicenter prospective cohort trial to compare the efficacy and safety of infliximab (IFX) and corticosteroids(CS) when they was used as first-line therapy in UC patients.