The invention discloses a SONOS flash memory, a preparation method thereof, and an operation method thereof. The flash memory comprises a substrate, a source drain and a groove, wherein a tunneling oxide layer, a silicon nitride trap layer, a block oxide layer and a polysilicon control grid are positioned on the groove in order. The flash memory is characterized in: that the substrate is lightly doped silicon; and the source drain comprises different doped types consisting of a P+ region and an N+ region. Compared with the prior standard CMOS technologies, the flash memory has better compatibility. As common SONOS flash memories, the flash memory in the invention is provided with good maintenance characteristics. Meanwhile, the flash memory of the invention has an ideal small size and can effectively improve programming efficiency, reduce power consumption, and inhibit the tunneling effects.