A new multilayer film consisting of Mo/Si/C has been fabricated by magnetic sputter deposition. Its thermal stability and reflectivity(near Brewster angle 45° incidence) have been researched using synchrotron radiation at Beijing Synchrotron Radiation Facility (BSRF). It was found that the reflectivity achieved 42% (at 45°

92eV) before the thermal treatment

thermal stability was increased because of the C sublayer’s entering

and its reflectivity was 6.8% at 97eV after annealing at 600 ℃. Due to the diffusion of amorphous carbon in interface layer

the structure of Mo/Si/C multilayer film was changed

and the double diffraction peaks during low-angle X-ray diffraction (LAXD) were observed.