An anti-PD1 (programmed cell death 1) monoclonal antibody or an antigen-binding fragment thereof, a pharmaceutical composition thereof and use thereof. The heavy chain variable region of the monoclonal antibody comprises CDRs (complementary determining region) of amino acid sequences as shown in SEQ ID NO:9-11; and/or the light chain variable region of the monoclonal antibody comprises CDRs of amino acid sequences as shown in SEQ ID NO:12-14. The monoclonal antibody can bind to PD1 specifically, relieve immunosuppression of PD1 on an organism specifically and activate T lymphocytes.