BiOBr　is　an　unstable　semiconductor　under　heating　condition.　Influence　of　calcination　temperature,　time　and　atmosphere　on　the　crystallinity,　surface　OH　groups　and　phase　transformation　of　BiOBr　was　investigated.　The　effects　of　structure　of　the　photocatalyst　on　photocatalytic　activity　in　degradation　of　acid　orange　II　under　visible　light　irradiation　were　examined.　The　prepared　samples　were　characterized　by　X-ray　diffraction,　thermogravimetry,　scanning　electron　microscopy,　Fourier　transform　infrared　spectroscopy　and　UV-Vis　diffuse　reflectance　spectra.　Results　show　that　in　air　atmosphere,　the　calcination　at　temperature　below　500℃　obviously　increases　the　crystallinity　of　BiOBr,　thus　promotes　its　activity.　At　calcination　temperature　of　600-650℃,　BiOBr/Bi24O31Br10　mixed　phases　appear.　The　formation　of　BiOBr/Bi24O31Br10　remarkably　increases　activity.　When　temperature　reaches　750℃,　BiOBr　transforms　to　α-Bi2O3.　The　produced　α-Bi2O3　exhibits　good　visible　light　absorption　but　poor　activity　due　to　sintering.　The　calcination　in　vacuum　increases　the　crystallinity　of　BiOBr,　but　decreases　the　surface　OH　groups　of　the　sample,　which　is　adverse　to　increasing　activity.　©,　2015,　Editorial　Office　of　Transactions　of　Materials　and　Heat　Treatment.　All　right　reserved.