OPBP-1 is a D-peptide developed through phage display screening, molecular docking, and molecular dynamics simulations. It exhibits high stability, strong antitumor activity, and oral bioavailability. OPBP-1 selectively binds to the PD-L1 protein, significantly blocking the interaction between PD-1 and PD-L1, which helps restore and enhance T lymphocyte function while reducing the proportion of myeloid-derived suppressor cells (MDSCs), counteracting tumor-induced immune evasion. OPBP-1 is applicable for research in cancer immunotherapy.