The emergence of hybrid nanostructures has paved a novel path for the development of nanotechnology and next-generation quantum devices. In this study, we report a remarkable enhancement of nonlinear diffraction achieved within a hybrid artificial molecule consisting of a semiconductor quantum dot (SQD) and a metal nanoparticle (MNP). Our findings reveal that the optical nonlinear properties of the hybrid system can be substantially enhanced due to the plasmon resonance of MNP. Specifically, reducing the interparticle distance and SQD's size while increasing the MNP's size leads to a significant enhancement in the nonlinear phase modulation of the hybrid system. Meanwhile, the absorption spectra exhibit a redshift accompanied by linewidth broadening under the SQD-MNP coupling interaction controlled by geometric parameters, indicating plasmon-exciton energy transfer. On this basis, it is validated that the enhanced nonlinear phase modulation greatly improves the self-imaging visibility and the signal-to-noise ratio, and extends the near-field pattern over more Talbot lengths. We also demonstrate that the far-field diffraction efficiency is tunable via the coupling interaction between the artificial molecule and external fields, which is determined by the geometric structure, photon detuning, and Rabi frequency. For instance, the first-order diffraction efficiency can be increased from 39.58% to 55% if the geometric parameters of the hybrid system satisfy the threshold in non-resonance conditions. Such plasmon-enhanced optical lattices show potential for applications in all-optical modulators and all-optical switches operating at few-photon levels, and may also afford a novel perspective for the design and development of nanophotonics circuits and topological photonic devices.