Objective:To obtain a high specificity and high affinity anti-human PD-L1 monoclonal antibody which can be used for clinical diagnosis and block PD-L1 and PD-1 binding.Methods:BALB/c mice were immunized with recombinant PD-L1 protein.The positive cell clones stably secreting anti-human PD-L1 monoclonal antibody were obtained by classical hybridoma cell fusion technique.The specificity,affinity,subtype and other characteristics of the antibody were identified by ELISA.Immunofluorescence and indirect immunofluorescence were used to detect the tumor cells.Antibody blocking activity was confirmed by tumor killing test.Results:Two cell strains stably secreting monoclonal antibodies against human PD-LI were screened out.Abl and Ab2 had high titer and affinity.The antibody titers were 1:2.56×106 and 1:3×105,and the affinity was 1.5×109 L/mol and 2.5×10s L/mol respectively.There was no cross reaction between these two antibodies and PD-L2.Immunoblotting,indirect immunofluorescence confirmed that the antibody can be used to the diagnosis.Experiment showed that PD-L1 antibodies can increases tumor-killing activity of CIK cells.Conclusion:Two hybridoma cell lines capable of stably secreting highly specific and high affinity anti-human PD-L1 monoclonal antibody are obtained.They can specifically bind to PD-L1 molecules on tumor cells and can be used to the diagnosis of tumor phenotype and prognosis.Antibody blocking function can be applied to combined CIK cell immunotherapy.