A method of constructing a transposon capable of introducing an exogenous gene into host cells in the presence of a transposase, wherein the host cells are mammalian or insect cells, the method comprising: respectively transfecting the host cells with a control plasmid and a first to a fourth plasmids, wherein, the control plasmid consists essentially of, a gene cassette, which comprises a promoter of SEQ ID NO: 5 and a reporter gene operably linked to the promoter; and the first to the fourth plasmids consist essentially of, the gene cassette and, respectively, a first to a fourth terminal repeats disposed upstream of the gene cassette, wherein the first to the fourth terminal repeats respectively consist of the nucleotide sequences of SEQ ID NOs: 1 to 4; determining a control expression level of the reporter gene of the control plasmid in the host cells and respective expression levels of the respective reporter genes of the first to the fourth plasmids in the host cells; and constructing the transposon that consists essentially of, (i) an expression cassette comprising a non-prokaryotic promoter and the exogenous gene operably linked to the non-prokaryotic promoter, (ii) a first selected terminal repeat, which is one of the first to the fourth terminal repeats that elicits an expression level closest to the control expression level, and (iii) a second selected terminal repeat, wherein, when the first selected terminal repeat is the first or the third terminal repeat, the first selected terminal repeat is disposed upstream of the expression cassette, and the second selected terminal repeat is the second or the fourth terminal repeat that is disposed downstream of the gene cassette; or when the first selected terminal repeat is the second or the fourth terminal repeat, the first selected terminal repeat is disposed downstream of the expression cassette, and the second selected terminal repeat is the first or the third terminal repeat that is disposed upstream of the gene cassette. respectively transfecting the host cells with a control plasmid and a first to a fourth plasmids, wherein, the control plasmid consists essentially of, a gene cassette, which comprises a promoter of SEQ ID NO: 5 and a reporter gene operably linked to the promoter; and the first to the fourth plasmids consist essentially of, the gene cassette and, respectively, a first to a fourth terminal repeats disposed upstream of the gene cassette, wherein the first to the fourth terminal repeats respectively consist of the nucleotide sequences of SEQ ID NOs: 1 to 4; the control plasmid consists essentially of, a gene cassette, which comprises a promoter of SEQ ID NO: 5 and a reporter gene operably linked to the promoter; and the first to the fourth plasmids consist essentially of, the gene cassette and, respectively, a first to a fourth terminal repeats disposed upstream of the gene cassette, wherein the first to the fourth terminal repeats respectively consist of the nucleotide sequences of SEQ ID NOs: 1 to 4; determining a control expression level of the reporter gene of the control plasmid in the host cells and respective expression levels of the respective reporter genes of the first to the fourth plasmids in the host cells; and constructing the transposon that consists essentially of, (i) an expression cassette comprising a non-prokaryotic promoter and the exogenous gene operably linked to the non-prokaryotic promoter, (ii) a first selected terminal repeat, which is one of the first to the fourth terminal repeats that elicits an expression level closest to the control expression level, and (iii) a second selected terminal repeat, wherein, when the first selected terminal repeat is the first or the third terminal repeat, the first selected terminal repeat is disposed upstream of the expression cassette, and the second selected terminal repeat is the second or the fourth terminal repeat that is disposed downstream of the gene cassette; or when the first selected terminal repeat is the second or the fourth terminal repeat, the first selected terminal repeat is disposed downstream of the expression cassette, and the second selected terminal repeat is the first or the third terminal repeat that is disposed upstream of the gene cassette. when the first selected terminal repeat is the first or the third terminal repeat, the first selected terminal repeat is disposed upstream of the expression cassette, and the second selected terminal repeat is the second or the fourth terminal repeat that is disposed downstream of the gene cassette; or when the first selected terminal repeat is the second or the fourth terminal repeat, the first selected terminal repeat is disposed downstream of the expression cassette, and the second selected terminal repeat is the first or the third terminal repeat that is disposed upstream of the gene cassette.