Disclosed are a PEGylated compound obtained by site-directed mono-substitution of any amino group in the structure of an Exendin analog, a preparation method therefor, and a use thereof. In the present invention, a stable protection group Dde (N-α-1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl) is used, so that multi-substitution side reactions caused by the use of a labile protection group can be avoided, and preparation of the mono-substituted PEGylated Exendin analog with a high yield at a low reaction molar ratio can be achieved.
