Alkaline metal and alkaline earth metal borohydrides may provide ideal candidates for high-temperature superconductors. By replacing the metal element of the layered hexagonal structure Li2B2H in our earlier work, a novel energetically metastable hexagonal Na2B2H, designated as h-Na2B2H, was proposed at ambient condition. First-principles calculations suggest that h-Na2B2H may be prepared from Na3B20, Na, and H2 or from the pure elements by utilizing high-temperature and high-pressure technology. The h-Na2B2H exhibits the highest tensile stress of 24.2 GPa at a strain of 0.245 along the [1–10] direction among the four directions [100], [001], [110], and [1–10]. Electronic property calculations reveal that h-Na2B2H holds two-dimensional conductivity along B atom layers. Electron–phonon coupling calculation indicates h-Na2B2H has a Tc of 42.4 K with λ = 1.73. The superconductivity in h-Na2B2H primarily depends on the Na and B atomic vibrations. Thus, h-Na2B2H can be a potential superconducting material with 2D conductivity at atmosphere pressure.