Method of operating flash memory unit is provided. Flash memory unit includes first and second split-gate flash memory units, source and drain of first split-gate flash memory unit are connected with first and third bit lines respectively, source and drain of second split-gate flash memory unit is connected with second and third bit line respectively, first control gates of two split-gate flash memory units are connected with first control gate line, second control gates of two split-gate flash memory units are connected with second control gate line, word line gates of two split-gate flash memory units are connected with word line, method includes configuring voltages to first and third bit lines, word line, first and second control gate lines to select first storage bit in first split-gate flash memory unit and make first storage bit in to-be-read or to-be-programmed state; suspending second bit line; reading or programming first storage bit.