The invention belongs to the field of micro-nano semiconductor optoelectronic devices, and particularly relates to a phototransistor based on a ferroelectric gate dielectric and a thin layer MoS2 channel and a preparation method thereof. The phototransistor comprises a source electrode, a leakage electrode, a channel, a gate electrode, a gate dielectric, a metal pad, and a substrate. The source electrode and the leakage electrode are graphene, the channel is thin layer MoS2, and the gate dielectric is a PZT ferroelectric membrane. Compared with existing similar phototransistor, the phototransistor has the following advantages that first, a high dielectric coefficienet of the PZT ferroelectric membrane helps improve the adjustment performance of the gate electrode for a channel carrier; second, the PZT ferroelectric membrane can adjust the channel carrier with surplus polarity field strength, so that the power consumption of the device is lowered; third, compared with organic ferroelectric material P (VDF-TrFE), the PZT ferroelectric membrane has the advantages of high surplus polarity, low coercive field strength, stable property and compatibility with microelectronic process; and fourth, as the source electrode and leakage electrode, the graphene can improve the signal light transmittance, and improve the light response degree and gain of the device.