Electropolishing is a promising method for the post-treatment of the dental material Co-Cr alloy compared with the currently reported laser polishing by considering the damage-free surface and simplicity of the electropolishing method. The electrochemical properties of electropolishing the Co-Cr dental alloy is a critical issue in the process development. The electrochemical properties are first investigated by measuring the open circuit potential and the polarization curves and a limiting current density plateau region is identified, where the electropolishing is clarified. With the different applied potentials along the limiting current density plateau region, the electrochemical impedance spectroscopy spectra are studied to understand the mass transport limitation mechanism. The compact salt film model is confirmed to be responsible for the mass transport limitation in the electropolishing. Samples are electropolished with a constant applied potential, and a selective dissolution is achieved between the matrix phase and precipitate phase according to the electropolished surface topography. Moreover, the composition of the electropolished surface is analysed by the X-ray photoelectron spectroscopy spectra. Finally, a qualitative model is established to illustrate the electrochemical dissolution behaviour of the Co-Cr alloy electropolishing in the phosphoric acid-containing electrolyte. Graphic abstract Schematic diagram of the electrochemical dissolution behaviour in the electropolishing of Co-Cr alloy.