A thin film transistor memory provided by the present invention comprises a back gate, a barrier layer, a floating gate, a tunneling layer, a channel, a source electrode and a drain electrode, the back gate comprises a bottom gate structure and a side gate structure, the side gate structure is arranged on a part of the upper surface of the bottom gate structure to form an L-shaped structure, the barrier layer is arranged on the upper surface of the bottom gate structure, and the floating gate is arranged on the upper surface of the bottom gate structure. The floating gate is arranged on the upper surface of the barrier layer, the upper surface of the floating gate is flush with the upper surface of the side gate structure, the tunneling layer is arranged on the upper surface of the floating gate, the channel is arranged on the upper surface of the tunneling layer, the source electrode and the drain electrode are arranged on the upper surface of the channel, and the side gate structure is arranged on the upper surface of the channel. According to the technical scheme, energy band regulation and control can be carried out on the floating gate through the side gate structure, so that the electronic erasing speed is increased, the electronic erasing voltage is reduced, the power consumption can be reduced, and as the channel is not in contact with the floating gate, the memory is not easy to leak and higher in reliability. The invention also provides a preparation method of the thin film transistor memory.