Al2O3-SiO2　composite　membrane　was　prepared　by　sol-gel　process　using　aluminum　isopropoxide　and　tetraethoxysilane　as　raw　materials.　The　phase　constitution,　thermal　stability　and　the　pore　structure　were　characterized　by　means　of　XRD,　DTA-TGA,　IR,　BET　etc.　The　results　show　that　the　phase　constitution　of　the　composite　membrane　was　SiO2　and　γ-Al2O3　after　calcined　at　550°C　for　10　h,　and　the　particle　size　range　from　2　nm　to　4　nm.　The　XRD　results　of　the　composite　membrane　(Al2O3/SiO2　=　3:2)　calcined　at　different　temperatures　show　that　the　membrane　is　constituted　of　γ-AlOOH　and　γ-Al2O3　at　400°C,　γ-Al2O3　at　550°C　to　1150°C,　γ-Al2O3　and　α-Al2O3　at　1220°C,　mullite　and　α-Al2O3　at　1300°C.　Al2O3-SiO2　composite　membrane　is　constituted　of　Al-O　and　Si-O　networks,　and　no　Al-O-Si　network　found　membrane.　The　composite　membrane　has　high　thermal　stability,　and　the　pore　structure　of　the　membrane　can　influence　on　its　constitution　and　the　thermal　treatment　temperatures.