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In this article, the conduction current characteristics of polypropylene (PP) films treated by different dc electrical prestress are studied through experiments. The results show that the conduction current through the film is reduced by applying a strong homopolar dc prestress for 30 min, and the conduction current of the film decreases with the increase of homopolar prestress field. In contrast, the conduction current of the film increases with the application of heteropolar dc electrical prestress, and the conduction current increases with the increase of heteropolar prestress field. The relationship between conduction current and prestress is attributed to the effect of space charges. Under the action of homopolar dc prestress, homopolar space charges accumulate on the surface of the film, which reduce the electric field around the interface between the film surface and the electrode, reducing charge injection and the conduction current. In contrast, heteropolar dc prestress and heteropolar space charges have exactly the reverse effect. The research indicates that electrical prestress can adjust the injection and distribution of space charge, thereby regulating the conduction current characteristics of materials and improving the electrical properties of materials in practical use.