A method for expressing and preparing an antibody fusion protein, wherein said antibody fusion protein comprises: a light chain and a heavy chain of a first antibody that specifically binds to a first antigen; optionally wherein the heavy chain further comprises an intein-N moiety linked to its C-terminus; a light chain and the VH+CH1 portion of a heavy chain of a second antibody that specifically binds to a second antigen, wherein the C-terminus of the CH1 domain is fused to an IN moiety; an Fc chain from said second antibody, wherein the N-terminus of the Fc chain is linked to an Intein-C moiety; optionally, wherein said Fc chain further comprises an IN moiety linked to its C-terminus; a knob and a corresponding hole capable of associating with each other, the knob and hole being located in the interface of the CH3 domain of the heavy chain of the first antibody and of the CH3 domain of the Fc chain or vice versa; wherein the method comprises the following steps: A1: obtaining and amplifying the coding sequences of a "portion A antibody", said portion A antibody comprises said light chain and said heavy chain of said first antibody, and said Fc chain of said second antibody, in which the Intein-C moiety is fused to the N-terminus of said Fc chain; A2: constructing an eukaryotic or prokaryotic expression vector by whole-gene synthesis, wherein the vector comprises the coding sequences amplified in step A1 and obtaining the portion A antibody by expressing the vector via transient transfection or stable transfection; and B1: obtaining and amplifying the coding sequence of a "portion B antibody", said portion B antibody comprises said light chain and said VH+CH1 chain of said second antibody, in which the C-terminus of said VH+CH1 chain is fused to the Intein-N moiety; B2: constructing an eukaryotic or prokaryotic expression vector by whole-gene synthesis, wherein the vector comprises the coding sequences amplified in step B1 and obtaining the portion B antibody by expressing the vector via transient transfection or stable transfection; and D: obtaining the antibody fusion protein by subjecting the portion A antibody, the portion B antibody to protein trans-splicing in vitro. a light chain and a heavy chain of a first antibody that specifically binds to a first antigen; optionally wherein the heavy chain further comprises an intein-N moiety linked to its C-terminus; a light chain and the VH+CH1 portion of a heavy chain of a second antibody that specifically binds to a second antigen, wherein the C-terminus of the CH1 domain is fused to an IN moiety; an Fc chain from said second antibody, wherein the N-terminus of the Fc chain is linked to an Intein-C moiety; optionally, wherein said Fc chain further comprises an IN moiety linked to its C-terminus; a knob and a corresponding hole capable of associating with each other, the knob and hole being located in the interface of the CH3 domain of the heavy chain of the first antibody and of the CH3 domain of the Fc chain or vice versa; wherein the method comprises the following steps: A1: obtaining and amplifying the coding sequences of a "portion A antibody", said portion A antibody comprises said light chain and said heavy chain of said first antibody, and said Fc chain of said second antibody, in which the Intein-C moiety is fused to the N-terminus of said Fc chain; A2: constructing an eukaryotic or prokaryotic expression vector by whole-gene synthesis, wherein the vector comprises the coding sequences amplified in step A1 and obtaining the portion A antibody by expressing the vector via transient transfection or stable transfection; and B1: obtaining and amplifying the coding sequence of a "portion B antibody", said portion B antibody comprises said light chain and said VH+CH1 chain of said second antibody, in which the C-terminus of said VH+CH1 chain is fused to the Intein-N moiety; B2: constructing an eukaryotic or prokaryotic expression vector by whole-gene synthesis, wherein the vector comprises the coding sequences amplified in step B1 and obtaining the portion B antibody by expressing the vector via transient transfection or stable transfection; and D: obtaining the antibody fusion protein by subjecting the portion A antibody, the portion B antibody to protein trans-splicing in vitro. A1: obtaining and amplifying the coding sequences of a "portion A antibody", said portion A antibody comprises said light chain and said heavy chain of said first antibody, and said Fc chain of said second antibody, in which the Intein-C moiety is fused to the N-terminus of said Fc chain; A2: constructing an eukaryotic or prokaryotic expression vector by whole-gene synthesis, wherein the vector comprises the coding sequences amplified in step A1 and obtaining the portion A antibody by expressing the vector via transient transfection or stable transfection; and B1: obtaining and amplifying the coding sequence of a "portion B antibody", said portion B antibody comprises said light chain and said VH+CH1 chain of said second antibody, in which the C-terminus of said VH+CH1 chain is fused to the Intein-N moiety; B2: constructing an eukaryotic or prokaryotic expression vector by whole-gene synthesis, wherein the vector comprises the coding sequences amplified in step B1 and obtaining the portion B antibody by expressing the vector via transient transfection or stable transfection; and D: obtaining the antibody fusion protein by subjecting the portion A antibody, the portion B antibody to protein trans-splicing in vitro.