The invention provides a preparation method of alloyed hot-galvanized dual-phase steel, belonging to the technical field of high-strength cold-rolled hot-galvanized steel. Cold-rolled dual-phase DP steel comprises the following chemical components in percentage by weight: 1.3%-1.7% of Mn, less than or equal to 0.01% of P, 0.15%-0.25% of Mo, 0.15%-0.25% of Cr, 0.02%-0.04% of Nb, 0.07%-0.11% of C, 0.2%-0.5% of Si, 0.02%-0.07% of Als, less than or equal to 0.04% of N, 0.01% of S and the balance of Fe and impurities. According to the preparation method of the alloyed hot-galvanized dual-phase steel with excellent pore broadening performance, by adding a certain amount of Nb, martensite phases are refined and uniformly dispersed in a final microstructure; furthermore, by properly regulating the alloying temperature (520-560 DEG C), a proper amount of intermediate hard phase pearlite is generated, and the hardness difference between the hard martensite phases and a soft ferritic phase is reduced, so that the pore broadening performance of the dual-phase steel is improved.