Provided in the present invention are a 4-1BB antibody and a preparation method and the use thereof. In particular, provided in the present invention are a 4-1BB antibody, which has high affinity to 4-1BB protein, can effectively activate the signal downstream of the 4-1BB and significantly increase expression quantities of IFN-γ and IL-2 in human mixed lymphocytes or T lymphocytes, and can be used to treat cancers and autoimmune diseases.