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-a- 1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl) i s used, so that multi- substitution side reactions caused by the use of a labile protection group can b e avoided, and preparation of the mono -substituted PEGylated Exendin analog with a high yield at a low reaction molar ratio can b e achieved.
