Provided are a multispecific protein drug and a library thereof, a preparing method therefor and an application thereof. Specifically, a protein drug library is provided and comprises C different protein drug monomers, wherein the protein drug monomer comprises a protein drug component part and a nucleic acid component part connected with the protein drug component part, and the nucleic acid component part of one protein drug monomer establishes a double-stranded paired structure with a nucleic acid component part of at least one different protein drug monomer by means of complementation, thereby constituting a protein drug polymer, wherein C is a positive integer greater than or equal to 2.
