The invention discloses an aluminum oxide loaded PtCu monatomic alloy catalyst and a preparation method and application thereof. The catalyst takes Al2O3 as a carrier, takes Cu as an auxiliary, and loads a small amount of active components Pt; the mass percent of Pt is 0.025%-0.15%, and the mass percent of Cu is 5%-20%; and during preparation, a co-impregnation method is used, the Al2O3 carrier isimpregnated in an aqueous solution of chloroplatinic acid and copper nitrate, the PtCu / Al2O3 catalyst is obtained after drying and roasting and high-temperature reduction, and the catalyst has high activity and high stability, and is low in price and low in toxicity. The catalyst is suitable for reaction for producing olefin by dehydrogenation through low alkane, and is particularly suitable forreaction for producing propylene by dehydrogenation through propane in a hydrogenation atmosphere, the dehydrogenation activity is quite high under the condition of high temperature, the selectivity of the propylene can reach 90% or above, the stability is good, the use amount of Pt is small, the utilization rate is high, and compared with an industrial Pt series catalyst, the aluminum oxide loaded PtCu monatomic alloy catalyst is cheaper.