Co-Pt-C grain films with in plan magnetic anisotropy and large coercivity Hc were prepared by sputtering on Si substrates in multilayer form,with post-annealing in vacuum at 700℃ for 1?h. After annealing, Co-Pt particles trans form from amorphous to fcc CoPt3 and fct CoPt, and C remains in disorder state. Effects of Pt and C concentration on the magnetic properties of the films are studied. The maximum Hc is 430kA/m when the content of Pt is 70 vol% and the thickness of C layer is 0.4nm. The shoulder developed on the hysteresis loop is analyzed.