An antibody or a functional fragment thereof that specifically bind to PD-L1 with high affinity, a nucleic acid molecule that encodes said antibody or the functional fragment thereof, an expression vector and a host cell for use in expressing said antibody or the functional fragment thereof, and a method for producing said antibody or the functional fragment thereof. An immunoconjugate and a pharmaceutical composition containing said antibody or the functional fragment thereof, and a method for using said antibody or the functional fragment thereof to enhance the function of a T cell so as to up-regulate a cell-mediated immune response, for use in treating diseases caused by T cell dysfunction.
