BiOClxI1-x　composite　semiconductor　photocatalysts　were　synthesized　by　a　solvothermal　method.　The　thermostability　of　the　materials　and　the　relationships　among　their　phase,　morphology,　light　absorption　and　photocatalytic　performance　in　degradation　acid　orange　II　were　investigated　by　X-ray　diffraction,　scanning　electron　microscopy,　N2-physical　adsorption,　thermal　gravity　analysis,　Fourier　transform　infrared　spectroscopy,　and　ultraviolet-visible　diffusion　reflectance　spectroscopy,　respectively.　The　results　show　that　the　thermostability　of　the　BiOCl0.25I0.75　is　much　weaker　than　that　of　BiOCl　and　stronger　than　that　of　BiOI.　In　the　calcination,　a　Bi5O7I　phase　appears　with　the　gradual　release　of　I　element.　After　calcination　at　500,　the　compound　is　mainly　composed　of　bismuth　oxychloride.　Moreover,　the　spherical　structure　is　destroyed　and　the　surface　area　and　the　surface　OH　groups　are　lost.　The　photocatalytic　activity　of　BiOCl0.25I0.75　and　BiOCl0.50I0.50　are　greater　than　that　of　BiOCl　and　BiOI.　After　high-temperature　calcination,　the　photocatalytic　activity　decreases.　The　destruction　of　texture　and　the　loss　of　surface　area　and　I　element　can　lead　to　the　reduction　in　photocatalytic　activity.　©　2016,　Editorial　Department　of　Journal　of　the　Chinese　Ceramic　Society.　All　right　reserved.