As the core components of insulation systems or film capacitors, polymer dielectrics are widely used in electrical and electronic equipment and for energy storage. However, the electrical strength is always the bottleneck that limits further application. Therefore, a coating with a wide bandgap comprising of zinc oxide and polydimethylsiloxane is designed in this paper. Experiments show that the coating effectively improves the breakdown strength and flashover voltage. A Kelvin probe force microscope is used to determine the microscopic mechanism for performance improvement, the charge dissipation characteristics and the changes in trap parameters in the nanoscale regime. This shows that many shallow traps are introduced on the polymer surface after applying the coating, which dissipate the surface charges and increase the flashover voltage. First‐principles calculations indicate that the band gap of the coating is wider than that of the polymer dielectric, which explains the enhancement in breakdown field strength. This paper presents an efficient method for enhancing the electrical strengths of polymer dielectrics, which is crucial for their application. More importantly, the experimental and theoretical methods used to determine the microscopic mechanism and the conclusions obtained in this paper provide guidance for future research on polymer dielectrics. This paper proposes a wide‐bandgap zinc oxide (ZnO)−polydimethylsiloxane (PDMS) nanocoating that effectively improves the breakdown strengths and flashover voltages of widely used polymer dielectrics. This is essential for insulation systems in electrical and electronic equipment or energy storage film capacitors.