The invention discloses a preparation method of an in-situ synthesis carbonate ion-electron mixed conductor dual-phase membrane. A porous transition metal oxide skeleton is firstly prepared by adding a pore forming agent, then molten carbonate is dipped into the porous transition metal oxide skeleton, and the molten carbonate and the transition metal oxide react to form an electron conductive phase on an interface by controlling the temperature, so that an MECC (mixed electron and carbonate ion conductor) carbon dioxide separation membrane is prepared. In addition, the invention further discloses a product prepared according to the preparation method of the in-situ synthesis carbonate ion-electron mixed conductor dual-phase membrane. While the higher CO2 permeability is guaranteed, the membrane achieves long-term stability and mechanical performance, the problem about the preparation cost of the membrane is solved, and the preparation method can be widely applied to the fields of high-temperature CO2 separation, dry reforming of methane and the like.