Electric quadrupole resonance (EQR), a commonly available high-order Mie-type resonance in all-dielectric nanoparticles, suffers from weak field enhancement and thus inferior third-harmonic generation (THG). In this work, according to the intrinsic centrosymmetry of current distribution, mirror-induced EQR in a silicon disk is effectively generated by introducing a bottom metal film with the perfect electric conductor (PEC) mirror effect, manifesting preeminent capabilities of tailoring far-field scattering and enhancing near-field intensity. The beneficial THG by mirror-induced EQR is enhanced by more than 50-fold as compared to that of the typical EQR without the PEC mirror effect. Furthermore, the influence of the silicon Kerr effect on THG is investigated under increasing pump intensity, achieving maximal efficiency of 2.2 × 1 0 − 4 under pump intensity I 0 = 3 GW / cm 2 . This work opens possibilities of exploring new mirror-induced Mie-type resonances in hybrid nanostructures, finding important applications in frequency conversion, spectroscopy, and sensing at the nanoscale.