The invention belongs to the technical field of chemical catalysts, and specifically discloses a catalyst for preparing ethylene through ethane dehydrogenation under a carbon dioxide atmosphere, and a preparation method thereof. The existing catalyst has the shortages of high dosage of chromium, low selectivity of ethylene, low stability, and the like. According to the catalyst disclosed by the invention, small-crystal-grain all-silicon silicalite-1 with an MFI structure is taken as a support, chromium oxide is taken as an active component with a content of 0.3%-5.0%. A soluble chromium salt is taken as a precursor and introduced into the silicalite-1 zeolite by virtue of an impregnation method, and then is prepared into a supported catalyst through roasting during preparation. According to the preparation method disclosed by the invention, the impregnation method is adopted, and the preparation process is simple and convenient. The catalyst is used for a reaction of preparing ethylene through ethane dehydrogenation under a carbon dioxide atmosphere, and has the advantages of being simple in process, high in activity, high in selectivity and stability, and the like.