The present invention provides a PEGylated and fatty acid grafted chitosan oligosaccharide comprising a structural unit represented by the following Formula (I) and a structural unit represented by the following Formula (II) and synthesize method, wherein the chitosan oligosaccharide has a molecular weight of less than 200,000 Da, and a degree of deacetylation of 70%-100%, and part of free amino groups of chitosan oligosaccharide chain are replaced by a fatty acid or PEG, where n refers to degree of polymerization of the PEG, and R is an alkyl group having 11-21 carbon atoms. The grafting ratio of fatty acids is 1%-50%, and the grafting ratio of PEG is 0.05%-50%. The present invention also comprise a pharmaceutical composition comprising the PEGylated and fatty acid grafted chitosan oligosaccharide as a carrier, and use of the PEGylated and fatty acid grafted chitosan oligosaccharide in preparation of a pharmaceutical composition.
