This　paper　combined　the　activated　carbon　(AC)　with　TiO2　to　improve　the　photocatalyitc　efficiency　of　HCHO　for　the　mass　transfer　of　HCHO　on　the　surface　of　photocatalyst　TiO2　was　enhanced　and　the　local　concentration　of　HCHO　was　increased　by　the　absorption　of　AC.　The　experiment　results　shown　that　the　AC　has　the　performance　of　absorptive　saturation,　but　the　combination　of　AC　with　TiO2　can　delay　the　absorptive　saturation　of　AC　and　the　photocatalytic　efficiency　can　be　improved　simultaneously;　there　are　optimal　amount　of　TiO2　immobilized　on　the　AC;　the　photocatalyst　TiO2　film　coated　on　the　surface　of　AC　has　the　dual　characteristics　of　the　higher　activity　and　retentivity.　Those　results　will　be　the　theoretical　support　for　the　application　of　photocatalytic　technology.