The aim of research on neuromorphic computing is exploring artificial neuron and synaptic devices with high performance. In this context, two-dimensional (2D) materials have received broad attention due to their advantages of low power consumption and high electrostatic controllability. Here, we demonstrated an artificial synaptic transistor based on the 2D SnS2/T-layer van der Waals (vdW) heterostructure, where the T-layer refers to the 2D h-BN treated by O2 plasma. Relying on the charge trapping mechanism of the T-layer, synaptic characteristics such as the excitatory postsynaptic current, short-term plasticity, and long-term potentiation (LTP) are emulated. Moreover, these synaptic characteristics can be further modulated by light stimulation. Under the illumination of 820 nm wavelength, the nonlinearity of LTP is as low as −0.19, and the symmetricity is 39.4, which is superior to most of the 2D artificial synaptic devices reported to date. Our results demonstrate the great prospects of plasma-treated 2D vdW heterostructures for neuromorphic applications.