Provided is an anti-PD-L1 antigen binding protein, capable of binding to primate-derived PD-L1 with a KD value of 1×10−8 M or less. The antigen binding protein can block the binding of PD-1 and CD80 to PD-L1, stimulate the secretion of cytokines in immune cells, and can inhibit tumor growth and/or tumor cell proliferation. Also provided is a fusion protein, comprising human TGFBRII or a fragment thereof and the antigen binding protein. Also provided is an application of the antigen binding protein and/or the fusion protein in the prevention and treatment of tumors or cancers.