The invention provides a monoclonal antibody for a protein programmed death ligand 1 (PD-L1). The monoclonal antibody can be used for blocking linkage between the PD-L1 and a programmed death molecule 1 (PD-1), and thus the inhibiting effect of the PD-L1 on T cells expressing the PD-1 is blocked. According to the antibody provided by the invention, very effective reagents for treating a variety of cancers through regulating human immunologic functions are provided.