Phosphorene　has　attracted　intense　interest　due　to　its　unexpected　high　carrier　mobility　and　distinguished　anisotropic　optoelectronic　and　electronic　properties.　In　this　work,　we　unraveled　strain　engineered　phosphorene　as　a　photocatalyst　in　the　application　of　water　splitting　hydrogen　production　based　on　density　functional　theory　calculations.　Lattice　dynamic　calculations　demonstrated　the　stability　for　such　kind　of　artificial　materials　under　different　strains.　The　phosphorene　lattice　is　unstable　under　compression　strains　and　could　be　crashed,　whereas　phosphorene　lattice　shows　very　good　stability　under　tensile　strains.　Further　guarantee　of　the　stability　of　phosphorene　in　liquid　water　is　studied　by　ab　initio　molecular　dynamics　simulations.　Tunable　band　gap　from　1.54　eV　at　ambient　condition　to　1.82　eV　under　tensile　strains　for　phosphorene　is　evaluated　using　parameter-free　hybrid　functional　calculations.　Appropriate　band　gaps　and　band　edge　alignments　at　certain　pH　demonstrate　the　potential　application　of　phosphorene　as　a　sufficiently　efficient　photocatalyst　for　visible　light　water　splitting.　We　found　that　the　strained　phosphorene　exhibits　significantly　improved　photocatalytic　properties　under　visible-light　irradiation　by　calculating　optical　absorption　spectra.　Negative　splitting　energy　of　absorbed　H2O　indicates　the　water　splitting　on　phosphorene　is　energy　favorable　both　without　and　with　strains.　(Figure　Presented).　©　2014　American　Chemical　Society.