Abstract: The mechanism of the deposition of copper in non-image area was studied in this paper by electron micrography and X-ray electron spetrometry. It was shown that by immersing the sample into chloroauric acid soluhon continuous and tangled silver maments in the image area broke into tiny grains, but very little silver chloride and few gold specks was formed. The gelatin in the non-image area can reduce An³⁺. The reduction process might be divided into two steps.The first stop which is fast at the room temperature is the formation of An+ which is complexed by gelatin. The second step the speed of which can be accelerated by X—ray is the formation of gold sacks. Those complexed An⁺ and gold specks act as catalytic nuclei during the copper Physical development depositing copper in the non-boage area.