Based on Gaia XP spectra, we derive reliable and precise metallicity estimates for approximately 20 million giant stars. This dataset includes around 360,000 very metal-poor (VMP; [Fe/H] ≤ −2.0) stars and 50,000 extremely metal-poor (EMP; [Fe/H] ≤ −3.0) stars. Our results demonstrate the effectiveness of low-resolution spectra in determining stellar metallicities and provide a valuable resource for investigating the formation history and chemo-dynamical evolution of the Milky Way.