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 In order to improve the surface mechanical properties of QT500-7，the copperizing layer was prepared on the surface of QT500-7 by solid diffusion metallizing method.The diffusion behavior of copper in QT500-7 and its influence on the microstructure and hardness were studied by metallographic microscope，scanning electron microscope，hardness tester，respectively.According to the calculation results，the solid solubility of copper in ductile iron substrate enhanced with the increase of processing temperature，and the solid solubility was 0.56%(mass fraction) at temperature of 1 173 K.The diffusion distance of copper in ductile cast iron rose with the increase of diffusion temperature and diffusion time.The theoretical diffusion distance was 23 μm under the condition of 1 173 K insulation for 8 h.The experimental results showed that the diffusion of Cu in QT500-7 inhibited the growth of ferrite grains in the pearlite transformation stage，causing that the content of pearlite increased.The diffusion of copper into the ductile iron increased the amount of graphite at the prepared copperizing layer，and narrowed the gap between the amount of graphite in the core and the copperizing layer.Besides，the observed diffusion layer depth was 40 μm，larger than the theoretical diffusion distance of copper to the perfect crystal of iron.The hardness of the copperizing layer prepared on the surface of ductile cast iron was slightly higher than that of the original sample.