Abstract: A fusion protein for restoring functions of failing immune cells and application thereof. The fusion protein has a functional area for recognizing the failing immune cell and a functional area for conducting activation and amplification on the failing immune cell. The two functional areas are connected through a non-functional amino acid fragment with a certain length. The functional area for recognition uses the immune checkpoint specific antibody to recognize a phenotypic receptor of failing immune cells. The functional area for conducting activation and amplification adopts the cytokine or functionally-similar mutants, a ligand of the phenotypic receptor or functionally-similar mutants or an activating antibody to activate failing immune cells.