This paper discusses the main protective measures to avoid electrical corrosion failure of electromotor bearings, including the installation of grounded carbon brushes to channel the shaft current, and using insulated bearings to cut off the shaft current, and the advantages and disadvantages of them are explained respectively. For insulated bearings, the relationship among the thermal spraying process (powder particle size, spraying parameters) the coating structure (surface morphology and microstructure) and the coating properties of the Al2O3 ceramic coating are analyzed, and the methods of modifying the coating performance by doping other metal cation oxides or nanostructured powders are introduced. On this basis, the difficulties existing in the preparation technology of Al2O3 ceramic coating for insulated bearings are analyzed, and the main problems are summarized. Finally, the development trend of Al2O3 ceramic coating preparation technology for insulated bearings is prospected.