The present disclosure relates to a method for evaluating and screening a mutant inducing the high-efficiency formation of heterodimers from a human antibody heavy chain constant region mutant pair combination library in order to increase the yield of formation of human antibody heterodimeric heavy chain constant regions, and to a heterodimeric heavy chain constant region (heterodimeric F) library thereby. In addition, the present disclosure relates to a CH3 domain mutant pair in which the formation of the heterodimeric heavy chain constant regions is preferred in the library, to a heterodimeric heavy chain constant region pair comprising the CH3 mutant pair, to a bispecific antibody, to a fusion protein, and a use thereof. The CH3 domain mutant pair according to the present disclosure forms heterodimeric heavy chain constant regions at a high yield of at least 80-90%, and also has excellent thermal stability and retains binding ability to the heavy chain constant region receptor (FcRn). The CH3 domain mutant pair, the bispecific antibody comprising the same, or the antibody constant region fusion protein of the present disclosure can be usefully applied to the treatment or prevention of diseases associated with target antigens or target proteins.