Abstract: Fe_x Pt_100-x（x=30at%-60at%）nanocomposite films were deposited onto natural-oxidized Si（100） single crystal substrate by magnetron sputtering. The as-deposited films were annealed at 100-800℃.The structures, morphology, composition, and magnetic properties were measured by XRD, AFM, RBS and VSM. X-ray diffraction shows that the FePt nanocomposite films undergo a phase transformation from a disordered face-centered-cubic（fcc） phase to an ordered face-centered-tetragonal（fct） phase when annealed at 400-500℃, the coercivity of the annealed FePt alloy films is 306kA/m while average grain size is about 10 nm in sample annealed at 400℃. The adjustable coercivity and fine grain size indicate that this nanocomposites system has significant potential as recording media at extremely high density.