The invention discloses a sialic acid Neu5Ac derivative as well as a preparation method and application thereof, the structure of the derivative is shown as follows: R1 is selected from hydroxyl, methoxyl or substituted methoxyl; r2 is selected from an acetamido group, a substituted acetamido group, a benzamido group, a substituted benzamido group, an alkoxycarbonylamido group, a triazolyl group or a substituted triazolyl group; r3 is selected from a hydroxyl group, a methoxy group, a substituted methoxy group, an acetamido group, a substituted acetamido group, a sulfonamide group, a substituted sulfonamide group or a phosphamide group; a is or-(CH2) m-R4, and R4 is selected from amino, sulfydryl or azido; n is selected from 0, 1, 2, 3, 4, 5, 6 and 7; m is selected from 2, 3, 4, 5, 6, 7, 8, 9 and 10. The derivative provided by the invention not only can be combined with the S protein on the surface of the new coronavirus in a high-affinity manner, but also is endowed with wider application including detection of the new coronavirus, treatment of new coronapneumonia and the like through a derivative functional side chain.