Memtransistor is a new multi-terminal device which combines the properties of memristor and field effect transistor and simultaneously realizes information storage and processing. In this paper, the multilayer MoS₂ is prepared by micromechanical exploration method, then the back gate MoS₂ memtransistor with field effect transistor structure is fabricated, and the resistive switching characteristics and mechanism of the device under electric field, light field and their synergistic regulation are systematically studied. The experimental results show that the multilayer MoS₂ memtransistor has excellent bipolar resistance behavior and good cycle durability. Under the control of gate voltage, the switching ratio of the device can be tuned in a range of 10⁰－10⁵, up to 1.56 × 10⁵, which indicates that the device has a strong gating effect. Under the control of light illumination, the resistance characteristics of the device are strongly dependent on the incident wavelength. When photoelectric synergistic regulation is performed, the device displays excellent four-terminal control capability, and the switching ratio is enhanced up to 4.8 × 10⁴. The mechanism of resistive switching characteristics can be attributed to the changes of charge capture state and Schottky barrier height at the interface between MoS₂ and metal electrodes, and the continuous photoconductance effect caused by photogenerated carriers in MoS₂ channel.