Recently,two-dimensional borophene has been synthesized on silver substrate[1] and has attracted much attention.It is reported that borophene can be stabilized by full hydrogenation[2].A first principles study has been performed to study the mechanical,elastic properties,electronic structure and phonon instability of full hydrogenated borophene(called as borophane).The uniaxial tensile strains along a,b direction and biaxial tensile strains have been considered.Our results show that mechanical properties along the three applied strains are highly anisotropic.The ultimate tensile strains are 0.11,0.30 and 0.25,respectively,under the uniaxial tensile strains along a,b direction and biaxial tensile strain.Furthermore,the phonon dispersion and band structure of borophane under the three applied strains have been calculated.Phonon dispersions of borophane under tensile strain indicate that borophane can withstand up to 5%,15%uniaxial tensile strain along a,b direction and 9%biaxial tensile strain,indicating that the failure mechanism of borophane is only phonon instability.The Dirac cones maintain well under the three applied strains.However,compared to Fermi level,the energy level of the Dirac point has shifted to higher energy under ≥7%uniaxial strain along a direction,corresponding to a zero-gap semiconductor to metal transformation.Our numerical results indicate that borophane shows superior mechanical properties and phonon stability along b direction.