A luminescent brightness compensation of sub-pixels of tri-electrode based field-emission display. The cathode conductive layers corresponding to sub-pixels constituting a pixel are arranged at various levels according to the respective luminescent efficiencies thereof. Thereby, the color with lower or higher luminescent efficiency obtains a stronger or weaker electric field between anode and cathode, respectively. Therefore, the different luminescent efficiency of three sub-pixels with primary color is compensated.