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After phosphate treatment, the surface of mechanical parts has color differences of film, roughness and no film, and the properties of phosphating film could not meet the process requirements. Through comparison and analysis of literature, it was found that the physical or chemical changes took place on the surface of parts while forming parts by various processing methods, which meant the surface structure, surface composition, surface stress and other states of the parts were changed; the differences of surface state had different effects on phosphating reaction rate. Therefore, different pretreatment methods should be adopted for various surface states during phosphate treatment of mechanical parts to improve the phosphating film formation condition. In this way, uniform phosphating film could be formed on the surface of parts.