The invention discloses a PtCu single-atom alloy catalyst supported by alumina and its preparation method and application. The catalyst uses Al 2 o 3 As a carrier, with Cu as an auxiliary agent, a small amount of active component Pt is loaded; the mass percentage of Pt is 0.025%-0.15%, and the mass percentage of Cu is 5%-20%; co-impregnation method is adopted during preparation, Will Al 2 o 3 The carrier is impregnated in an aqueous solution of chloroplatinic acid and copper nitrate, and after drying, roasting and high temperature reduction, PtCu / Al 2 o 3 The catalyst has high activity and high stability, low price and low toxicity. The catalyst of the present invention is suitable for the reaction of dehydrogenation of low paraffins to olefins, especially the reaction of propane dehydrogenation to propylene under a hydrogen atmosphere. The dehydrogenation activity is very high under high temperature conditions, the selectivity of propylene can reach more than 90%, and the stability is good. , and the amount of Pt is small, the utilization rate is high, and it is cheaper than industrial Pt-based catalysts.