We numerically solved the time-dependent Schrödinger equation (TDSE) for a hydrogen atom interacting with intense near-infrared laser fields to investigate the mechanism of below-threshold high-harmonic generation (HHG). The primary focus was on understanding the spectral features, particularly resonant structures, arising in the fifth harmonic region under specific driving conditions. Our simulations utilized a laser wavelength of 608 nm. At this wavelength, hydrogen atoms can resonantly absorb five photons, promoting electrons from the ground stateWe numerically solved the time-dependent Schrödinger equation (TDSE) for a hydrogen atom interacting with intense near-infrared laser fields to investigate the mechanism of below-threshold high-harmonic generation (HHG). The primary focus was on understanding the spectral features, particularly resonant structures, arising in the fifth harmonic region under specific driving conditions. Our simulations utilized a laser wavelength of 608 nm. At this wavelength, hydrogen atoms can resonantly absorb five photons, promoting electrons from the ground state \left|1\mathrms\right\rangle to the excited state \left|2\mathrmp\right\rangle. Concurrently, the atom can absorb additional photons leading to ionization. Crucially, due to the AC Stark shift induced by the intense laser field (laser dressing), some laser-dressed continuum states \left|\mathrmc\right\rangle become energetically degenerate with the laser-dressed \left|2\mathrmp\right\rangle state. High-harmonic radiation at the fifth harmonic frequency can then be emitted via two distinct quantum paths: 1) Bound-bound recombination: Direct recombination from the laser-dressed \left|2\mathrmp\right\rangle state back to the ground state \left|1\mathrms\right\rangle. 2) Continuum-bound recombination: recombination from the laser-dressed continuum states \left|\mathrmc\right\rangle (reached via ionization) back to \left|1\mathrms\right\rangle. Both pathways emit photons of identical energy corresponding to the fifth harmonic. Our important finding is that there is significant quantum interference between these two recombination channels. This interference is manifested in the spectrum as an asymmetric Fano lineshape of the fifth harmonic intensity profile. Furthermore, we demonstrate that the shape of this Fano resonance exhibits strong and controllable dependence on the intensity of the driving laser field. This study provides clear evidence that Fano quantum interference, typically associated with multi-electron correlations or autoionizing states in complex systems, can emerge in the fundamental single-electron hydrogen atom system under the condition of intense laser field. The interference arises directly from the coherent superposition of the bound-bound and continuum-bound recombination pathways caused by laser-induced degeneracy. Importantly, by adjusting the laser intensity the spectral profile of the Fano resonance can be actively manipulated, providing a novel method for coherently controlling the harmonic emission in simple atomic systems.