Abstract: Objective　The method of "molecular docking - molecular dynamics - in vitro pharmacology" was used to screen and optimize small molecule polypeptide compounds that can block PD-1/PD-L1 binding and have high anti-tumor activity. Methods Using the 5-peptide compound database constructed by our team and the three-dimensional structure data of the PD-L1 protein downloaded from the protein database (PDB), the peptide compounds obtained by flexible molecular docking using Molecular Operating Environment software. The molecular dynamics calculation and analysis of the compounds with the highest GWVI/WSA (generalized Born volume integral/weighted surface area) free energy change value (ΔG) were carried out, including the root mean square deviation (RMSD) of the position change of the weight atom and the interaction energy (the sum of Lennard-Jones potential and Coulombic energy). The blocking effect of ligand compounds on PD-1/PD-L1 binding was analyzed by the homogeneous time-resolved fluorescence (HTRF) technique. The co-culture system of Jurkat T lymphocytes and melanoma B16-F10 cells was established to explore the effect of compound ligands on the killing effect of T cells on tumors and the effect on the secretion level of IL-2 in the co-culture supernatant. Results The selected polypeptide compounds were analyzed by molecular dynamics, and the binding of RGGHA to RGGHH and PD-L1 was stable. There are many kinds of interactions between RGGHA and PD-L1，which can compete with PD-1 ligands to bind Asp122, Try123 and Lys124 sites of the PD-L1 protein and block PD-1/PD-L1 signal transduction. HTRF experiments showed that the binding inhibition rate of RGGHA to PD-1 and PD-L1 was 58.38%, and that of RGGHH was 42.73%. In addition, we established a co-culture system of Jurkat T lymphocytes and melanoma B16-F10 cells to explore the immunostimulatory effect and mechanism of peptides. The results show that RGGHA and RGGHH can significantly increase the secretion level of IL-2, improve the killing ability of T cells against tumor cells and activate the tumor immune microenvironment. Conclusions The study found that the polypeptide compounds RGGHA and RGGHH can effectively block the PD-1/PD-L1 interaction and reactivate the anti-cancer immune response, which can be used as lead compounds for new drug development.