The reaction of corrosive sulfur present in transformer oil with the copper winding results in the formation of copper sulfide (Cu₂S), and this process is intimately associated with the occurrence of partial discharge (PD) phenomena in power transformers. The development process of partial discharges in oil-paper insulation under Cu₂S deposition conditions and its influencing laws were investigated. A hydrodynamic drift-diffusion model and a bipolar charge-carrier transport model were combined to analyze the development of PD under cylindrical plate electrode geometries. Charge density cloud maps of PD processes in oil-paper system under Cu₂S deposition in slightly inhomogeneous electric field conditions were obtained. As the applied voltage increases, the oil molecules near the column electrode were first ionized into positive ions and electrons, and then the oil molecules near the deposition begin to be ionized. An increase in the thickness of Cu₂S deposits leads to an elevation in the electric field strength within the oil gap, subsequently exacerbating the discharge phenomenon and resulting in a greater local charge density. The wider deposition of Cu₂S promotes the diffusion of charge along its surface. The study has revealed the physical mechanisms and operating laws underlying the PD induced by Cu₂S deposition in a slightly inhomogeneous electric field, thereby providing a theoretical reference for the further development of suppression techniques for Cu₂S deposition-related discharges.