An antibody or an antigen-binding fragment thereof and a single-domain antibody or an antigen-binding fragment thereof that can specifically bind to CTLA4, and an immunoconjugate, a pharmaceutical composition and a multispecific molecule comprising the antibody or the antigen-binding fragment thereof. Furthermore, the present invention also relates to a multispecific molecule that can specifically bind to CCR8 and CTLA4 and the use thereof.