As fuel of star formation, the cold gas plays an important role in the evolution of galaxies. In this talk, I will briefly introduce our recent work on estimating the amount of cold gas in star-forming and quenched galaxies, as well as how it regulates the star formation processes. We took advantange of the completed ALFALFA survey and stacked the atomic neutral hydrogen (HI) spectra to obtain the average HI masses for different populations. We find that the quenched galaxies have significantly lower HI masses, compared to their star-forming counterparts with similar masses. The star formation and quenching of central galaxies are directly regulated by the available HI reservoir. We also investigate the role of AGN feedback in depleting the cold gas in both observation and hydrodynamical simulations.