The invention relates to application of a polypeptide compound having double agonist effects on a glucagon-like peptide-1 receptor and a glucagon receptor. The polypeptide compound has the characteristics of high enzymolysis stability, high bioactivity, no adverse reaction, etc., can alleviate abnormal rise in the levels of total cholesterol and triglyceride in blood induced by diabetes and high-meal diet, lowers the level of liver enzyme, improves liver damage and fibrosis stage and is applicable to prevention or treatment of diseases like non-alcoholic fatty liver diseases, hyperlipidemia and arteriosclerosis.