A fucosylated chondroitin sulfate oligosaccharide having the structure as shown in J, and further disclosed is a method for preparing the fucosylated chondroitin sulfate oligosaccharide : using a chondroitin sulfate A salt as a raw material, sequentially performing enzymolysis, a group protection operation, and glycosylation to synthesize the oligosacchaide compound; the certainty of the described structure allows said oligosaccharide to be applied to the medical field.