Fe53Pt47 nanocomposite films have been deposited on naturally oxidized Si(100) substrates by magnetron sputtering. The relationship between the grain size, the magnetic interaction and the annealing temperature have been studied. The FePt films exhibit magnetically hard property with average grain size of about 20 nm after annealing at 400℃, and exchange spring behavior was found in the sample because it is composed of magnetically soft γ-FePt phase and hard γ2-FePt phase. As the annealing temperature increases, the content of the γ2-FePt phase increases, at the same time, the grain size gets large, and the exchange spring behavior in some particles was discoupled. The static magnetic interaction only occur between the FePt particles in the film annealed at 600℃.