Transparent mullite ceramic film was prepared by Sol Gel. The Structure and cation ion coordination state of transparent film were studied through analysis of O 1s 、 Al 2p and Si 2p by XPS. The study shows that aluminum is mainly octahedron of AlO 6 and silicon is tetrahedron of SiO 4 in dry gel, and AlO 6 are translated to AlO 4 with increasing of temperature, causing the change of transparent film structure.