This study employs simulations to analyze how the waveguide thickness and the structural parameters of two asymmetric gratings—including their period, size difference, and spacing—affect waveguide mode resonances and bound states in the continuum (BICs). The results show that both the waveguide thickness and grating period can effectively tune the resonance wavelength. When an offset causes one grating to enlarge and the other to shrink, the two spectral peaks shift in opposite directions, accompanied by an interchange of the electric field distributions. Furthermore, two absorption mechanisms are investigated. Using metallic gratings can convert reflection peaks into absorption peaks, reaching over 60% absorption, while adding a monolayer graphene layer yields up to 43% absorption. Both approaches maintain quality factors above 10⁵. These findings provide insights for the design of high-Q photonic structures and lay the groundwork for future experimental verification and practical implementation.