A multifunctional polypeptide chain or a protein. A polypeptide chain X, comprising an antigen 1 binding domain R1, an auxiliary peptide chain linking domain R2 and an antigen 2 binding domain R3. The auxiliary peptide chain linking domain R2 is a cytokine or a cytokine binding domain in a cytokine receptor. A protein, which is a heterodimer composed of the polypeptide chain X as a main peptide chain and an auxiliary peptide chain Y. The auxiliary peptide chain Y comprises an antigen 3 binding domain R4 and a main peptide chain X linking domain R5, or the auxiliary peptide chain Y is the main peptide chain linking domain R5. The multifunctional protein mediates specific cell killing by binding to different tumor antigens with the two antigen binding domains of tumor-associated antigens therein. The multifunctional protein can function as a cytokine by introducing a cytokine or a cytokine receptor complex.
