We report resonance gradient metasurfaces, which show nearly continuous tunability of the high-Q resonance over a broadband wavelength range. The spectral tuning of the high-Q resonance is realized by gradually scaling the unit cell’s geometrical parameters along one coordinate of the metasurface. By using the gradient metasurface and a tunable infrared laser, a resonantly enhanced tunable generation of optical harmonics over a broad spectral range is realized (Adv. Mater. 2024, 36, e2307494). Additionally, broadband biosensing and control of vibrational light-matter coupling by using the gradient metasurface were demonstrated. This research establishes the groundwork for innovative light-generating devices and biosensors.