Using first-principles calculations based on density functional theory (DFT), we investigate the potential hydrogen storage capacity of the Na-decorated net-Y single layer nanosheet. For double-side Na decoration, the average binding energy is 1.54 eV, which is much larger than the cohesive energy of 1.13 eV for bulk Na. A maximum of four H2 molecules can be adsorbed around each Na with average adsorption energies of 0.25-0.32 eV/H2. Also, H2 storage gravimetric of 8.85 wt％is obtained, and this meets the U.S. Department of Energy (DOE) ultimate target. These results are instrumental in seeking a promising hydrogen energy carrier.