The invention is in the field of biotechnology. Specifically it describes the application and pharmaceutical composition of Reg4. The invention describes the applications of the protein as following in (a) or (b) in preparing drugs for treating acute pancreatitis: (a) the protein whose amino acid sequence is shown as SEQ ID NO. 1, or bioactive fragments, or analogs; (b) the proteins whose amino acid sequence have at least 70% homology comparing with amino acid sequence described in (a) and have activity for treating acute pancreatitis. The protein described in this invention treats acute pancreatitis effectively and may provide new therapy for treating acute pancreatitis clinically.