The invention discloses a new-structure material-ytterbium-magnesium-indium oxide and a preparation method thereof, and belongs to the technical field of preparation of quantum topological materials.A molecular formula of the ytterbium-magnesium-indium oxide is YbMgInO4, and the ytterbium-magnesium-indium oxide has a monoclinic crystal structure. The preparation method is characterized by takingytterbium oxide powder, magnesium oxide powder and indium oxide powder as raw materials and synthesizing on a high-temperature high-pressure device, wherein the synthetic pressure is 5.5GPa, the temperature is 1873 to 2073 K, and temperature preservation and pressure preservation can be carried out for 15 to 30 minutes. The preparation method disclosed by the invention is implemented in an anhydrous and improver-free environment, unnecessary impurities can be prevented from appearing, and the obtained monoclinic crystal ytterbium-magnesium-indium oxide is high in purity; the used high-temperature high-pressure device is already used for producing diamond to a large extent, the operation is simple, and industrialization can be more quickly implemented.