Abstract: Disclosed are an rk polypeptide radiopharmaceutical targeting HER2, and a preparation method therefor. The rk polypeptide radiopharmaceutical comprises an rk polypeptide dimer and a radionuclide, wherein the radionuclide marks the rk polypeptide dimer by means of a chelating agent, the rk polypeptide dimer is a polypeptide dimer formed by connecting PKM and rk polypeptide monomers and then dimerizing two rk polypeptide monomers connected to the PKM; each rk polypeptide monomer is a D-type amino acid linear eight-membered polypeptide, and the sequence of the rk polypeptide monomer is as follows: Arg-Asn-Trp-Glu-Leu-Arg-Leu-Lys; and the PKM represents a pharmacokinetic modifying molecule. The radiopharmaceutical is used for imaging diagnosis of HER2-positive tumor patients, and medication guidance and real-time therapeutic effect monitoring of patients treated by monoclonal antibodies of the anti-cancer drug trastuzumab.