Gold (Au) nanoparticles were prepared on Au-film-coated K9 glass and silicon substrates by direct current (DC) magnetron sputtering and thermal annealing treatment. The effects of substrate material, annealing temperature, and time on morphologies of Au nanoparticles were investigated, and the formation mechanism of Au nanoparticles was discussed. The experimental results indicate that silicon substrate is more suitable for the formation of Au nanoparticles. On a silicon substrate, Au nanoparticles formed with good spherical shapes at temperature over 700℃. It was also found by spectral analysis that the field enhancement factor of the island-shaped Au particles was smaller than that of the granular Au particles; the better the spherical shape as well as the smaller the size and spacing of Au particles, the higher the light absorption rate;the absorption peak had a red shift with increasing particle size and spacing.