The invention relates to a dendritic platinum-palladium alloy nanometer catalyst as well as a preparation method and application thereof. A structural formula of the dendritic platinum-palladium alloy nanometer catalyst is PtxPd100-x, and x is not less than 0 and not more than 100; the dendritic platinum-palladium alloy nanometer catalyst is prepared from platinum pentanedionate and palladium pentanedionate in an oleylamine solution under conditions of a temperature of 50-90 DEG C and the presence of H2. The dendritic platinum-palladium alloy nanometer catalyst is used for hydrogenation reduction of a methanol fuel cell anode catalyst and a nitrocompound. The dendritic platinum-palladium alloy nanometer catalyst shows a relatively strong poisoning resistance and relatively high electric catalysis stability in a process of an electric catalytic oxidation of a methane solution with a certain concentration, can realize the hydrogenation reduction of the nitrocompound at a low temperature and a normal pressure, has a dormant advantage especially for the hydrogenation reduction of polynitro compounds, and can be used for effectively reducing the energy consumption.