Palladium-copper nanoparticles which average particle size less than 10 nm were deposited on alumina balls by supercritical fluid deposition (SCFD) method. using alumina balls as carrier and palladium acetylacetonate and copper acetylacetonate as precursors. High-angle annular dark field-scanning transmission election microscope (HAADF-STEM), X-ray diffraction (XRD) and weighing methods were used to characterize the loading status and particle size distribution of palladium-copper nanoparticles. The results showed that the deposition temperature and the deposition pressure had important effects on the particle size of palladium-copper nanoparticles. The average particle size of palladium-copper nanoparticles could reach 2.37 nm at 65 ℃ and 15 MPa. For a fixed amount of metal precursor, the deposition time had an optimal value. The selection of co-solvent affects the particle size distribution and the average particle size of palladium-copper nanoparticles. At 65 ℃ and 15 MPa, when 8 mL of dichloromethane was used as a co-solvent, the average particle size of the palladium-copper nanoparticles was reduced to 1.81 nm. With the increase of Pd theoretical loading, the average particle size of palladium-copper nanoparticles decreased first and then increased. When Pd theoretical loading was 0.50%, the average particle size reached the minimum value 1.81 nm.