The disclosure discloses a chemical synthesis method of oligosaccharides of a Pseudomonas aeruginosa serotype O11 O-antigen, and belongs to the field of chemistry. The disclosure includes constructing an O-antigen trisaccharide by using a D-glucose building block, an L-fucosamine building block and a D-fucosamine building block; wherein the D-glucose building block or the L-fucosamine building block is linked with the D-fucosamine building block through a 1,2-α-cis-glycosidic bond, the D-glucose building block is linked with the L-fucosamine building block through a 1,2-β-trans-glycosidic bond, and the construction of the 1,2-α-cis-glycosidic bond is conducted in a mixed solvent; and the mixed solvent includes two or more of dichloromethane, diethyl ether and thiophene. According to the method of the disclosure, D-mannose is taken as a raw material, D-fucose is obtained simply, conveniently and efficiently, depending on suitable mixed solvents, the uniform construction of a cis-glycosidic bond of the D-fucose is achieved, the stereoselectivity can be up to 100%, and a very good application prospect in the aspects of the development of novel medicines and vaccines against Pseudomonas aeruginosa and the like is achieved.