The excellent strength, toughness, and corrosion resistance of high-strength stainless steel has led to its extensive use in the chemical, nuclear, aerospace, and aviation industries. To shape this hard-to-cut material, electrochemical machining is a promising process. However, few reports have focused on the electrochemical dissolution behavior of high-strength stainless steel. Therefore, we focus herein on the electrochemical dissolution behavior of S-04 high-strength stainless steel in NaNO(3)aqueous solution. The current efficiency indicates that current density can be divided into three regions (I, II, and III). Interestingly, a black machined surface appears in regions II and III, and the machined surface is shiny for region III. X-ray photoelectron spectroscopy indicates that the black machined surface is mainly due to the presence of Fe3O4. In addition, gamma-Fe2O3 was also detected on the black machined surface in region III, whereas both gamma-Fe2O3 and alpha-Fe2O3 were also detected on the black machined surface in regions I and II. Moreover, dissolution morphologies examined by SEM/EDX at different current densities and machining times showed that a good surface finish of the S-04 specimen can be obtained in region III. Finally, grooves with black surfaces in regions II and III were obtained by electrochemical milling. Graphic abstract