Abstract: A recombinant fusion protein, a nano-assembly, and preparation methods therefor and the use thereof. The nano-assembly is constructed from at least one recombinant fusion protein and a hydrophobic degradable polyester and a derivative thereof. The recombinant fusion protein comprises a single-chain antibody fragment, a linker peptide and an albumin having a hydrophobic region, wherein the single-chain antibody fragment has at least one of the effects of competitively binding to a target, inhibiting a signaling pathway, activating a signaling pathway, and targeting an antigen. The present disclosure further relates to a method for preparing a monoclonal antibody fragment-albumin recombinant fusion protein, and a method for constructing a nano-assembly. On the basis of the nano-assembly, a brand-new method for constructing a mono-specific, bispecific or multispecific antibody is provided, and the nano-assembly can be used for treating diseases such as tumors and autoimmune diseases.