Hard passive alloys, such as nickel-based superalloys, titanium alloys, and molybdenum alloys, are widely used as engine components, isothermal hot dies and forging tools, die castings, etc. in various industries. The finishing of these materials by traditional manual methods, especially in the manufacturing of dies and moulds, is both tedious and time-consuming. A new MREF-ECM (modulated reverse electric field electrochemical machining) polishing process is being developed for hard passive alloys surface finishing. The results obtained from the experimental study are reported in this paper. An important parameter, MREF-ECM electric field waveform is investigated to optimize the ECM polishing process for IN718.