Provided are a LAG-3 antibody, an antigen-binding fragment thereof, and a pharmaceutical application thereof. Further, provided are a chimeric antibody comprising a CDR of the LAG-3 antibody, a humanized antibody, a pharmaceutical composition comprising the LAG-3 antibody and the antigen-binding fragment thereof, and an application of the pharmaceutical composition as an antineoplastic drug. Particularly, provided is an application of a humanized LAG-3 antibody in preparation of drugs for treatment of diseases involving immune cells.