The invention provides a heterojunction composite material as well as a preparation method and application thereof. The heterojunction composite material is structured that a plurality of noble metalnanoparticles are attached to the surface of barium sulfate, wherein the grain sizes of barium sulfate are 1-3 [mu]m, the grain sizes of the noble metal nanoparticles are 3-10 nm, and the noble metalsare gold, silver or platinum. The preparation method comprises the following steps: attaching a compound containing M ions to the surface of barium sulfate by adopting an impregnating method; and then reducing the M ions of the compound containing the M ions on the surface of barium sulfate to M nanoparticles, wherein M is Ag, Au or Pt, and the grain sizes of barium sulfate are 1-3 [mu]m. According to the heterojunction composite material, micron order barium sulfate serving as a carrier of the noble metal nanoparticles has a large specific surface area, so that the noble metal nanoparticlescan be more uniformly attached to the surface of micron order barium sulfate. Meanwhile, the barium sulfate and the noble metal nanoparticles have a synergistic effect, so that the catalytic activityof the noble metal nanoparticles is improved.