A　photocatalyst　Sr0.4H1.2Nb2O6　center　dot　H2O　(HSN)　nanopolyhedra　with　high　surface　area　has　been　successfully　prepared　by　a　simple　hydrothermal　method.　The　as-prepared　samples　were　characterized　by　XRD,　BET,　SEM,　TEM　and　XPS.　The　electronic　structure　of　HSN　determined　by　DFT　calculations　and　electrochemical　measurement　revealed　that　HSN　is　an　indirect-bandgap　and　n-type　semiconductor,　respectively.　HSN　samples　showed　high　photocatalytic　activities　for　both　pure　water　splitting　and　the　decomposition　of　benzene.　The　rate　of　H-2　evolution　over　HSN　was　15　times　higher　than　that　of　P25　and　the　conversion　ratio　of　benzene　exceeded　twice　that　of　P25.　The　photocatalytic　activities　for　water　splitting　can　be　greatly　improved　by　loading　various　co-catalysts　on　HSN,　such　as　Au,　Pt,　and　Pd.　The　photocatalytic　mechanisms　were　proposed　based　on　the　band　structure　and　characterization　results　of　the　photocatalyst.