Selective recognition of short oligonucleotides at the single-molecule level is particularly important for early disease detection and treatment. In this work, polydopamine (PDA)-coated nanopores were prepared via self-polymerization as a solid-state nanopore sensing platform for the recognition of oligonucleotide C (PolyC). The PDA coating possesses abundant active sites, such as indole, amino, carboxyl, catechol, and quinone structures, which had interactions with short oligonucleotides to slow down the translocation rate. PDA-coated nanopores selectively interact with PolyC20 by virtue of differences in hydrogen bonding forces, generating a larger blocking current, while polyA and polyT demonstrated very small blockings. At the same time, PDA-coated nanopores can sensitively distinguish PolyC with different lengths, such as 20, 14, and 10 nt. The functionalization of PDA on the solid-state nanopore provides an opportunity for the rational design of the recognition surface for biomolecules.