The invention discloses a preparation method of a PtPd/Fe3O4 (platinum-palladium/ferroferric oxide) nanocatalyst and an application thereof in HECK reaction, and belongs to the technical field of nanocatalysts. The preparation method is characterized in that a catalyst carrier is magnetic Fe3O4 nanoparticles, and the average particle size is 18nm; the active components are Pt and Pd nanoparticles, and the average particle sizes are respectively 12nm and 10nm; the average mass percentages of Pt and Pd in the catalyst are respectively about 0.39% and 0.75%; the balance is Fe3O4 nanoparticles. The preparation method comprises the following steps of oxidizing and reducing FeCl3 6H2O into the Fe3O4 nanoparticles by a hydrothermal method; cleaning, and metering volume for use; using polymers of polyvinylpyrrolidone and the like as stabilizers, and reducing a certain ratio of chloroplatinic acid and chloropalladic acid by a reducing agent, so as to prepare a Pt-Pd sol; adding the treated Fe3O4 nanoparticles into the Pt-Pd sol, stirring, filtering, and drying, so as to finally prepare the Pt-Pd magnetic nanometer-supported catalyst. The catalyst prepared by the preparation method has higher catalytic activity in the Heck reaction.