The invention discloses an N-acyl group modified sialic acid (alpha-(2-6))-D-amino pyranose derivative and its synthetic method and use. The sialic acid (alpha-(2-6))-D-amino pyranose derivative shown in the formula (I) is synthesized from raw materials of D-galactosamine (glucose) and sialic acid and is coupled with a carrier protein or a polypeptide to form a glycoprotein (glycopeptide) conjugate. In a structure of the N-acyl group modified sialic acid (alpha-(2-6))-D-amino pyranose derivative, a derivative acyl group replaces an acetyl group and thus the structure is novel. The N-acyl group modified sialic acid (alpha-(2-6))-D-amino pyranose derivative has good activity in anti-tumor vaccines. A result of an experiment on mice shows that through structural derivatization, a carbohydrate antigen based vaccine can produce an effective immune response and a mass of antibodies and IgG/IgM is improved obviously. The antibodies can identify specifically tumor cells expressing STn and thus anti-tumor effects are realized. STn antigens can be expressed on multiple tumors and thus the N-acyl group modified sialic acid (alpha-(2-6))-D-amino pyranose derivative has a wide application scope.