TiO2/SiO2 was prepared by adsorption phase synthesis, and its photocatalysis on degradation of gaseous toluene was studied. The concentration of water added in preparation and temperature in calcination were changed to regulate formation of anatase TiO2. Ti contents in samples and grain size of anantase TiO2 were measured, and the catalytic activity in photodegrading gaseous toluene was characterized. The photocatalytic activity increased sharply when the calcination temperature increased to 500 degrees C or the volume of water added in preparation reached 1.5 mL. XRD analysis indicated that the crystal phase trails formation of TiO2 from anatase to rutile was restrained and TiO2 remained in the form of anatase even after being suffered at 900 degrees C. The high constant photocatalytic activity front 500 to 900 degrees C was attributed to the stability of anatase TiO2 in crystal size and phase transformation.