Post-annealing treatment for CoCrPt magnetic thin films were tried in different thermal conditions, by changing the time annealing procedure. Coercivity(H_c)improvement was achieved in every annealed sample compared with those as deposited, in which as high as 5210 Oe has been attained. In order to clarify the mechanism of this annealing treatment on the magnetic properties, x-ray diffraction(XRD)spectrums combined with the magnetic properties were carefully studied. Co and Cr lattice parameters were separately calculated from different crystal lattice plane. It was found that a axis lattice spacing of Co haxagonal structure also increases monotonically with increased annealing time. Simultaneously, c axis lattice did have any obvious trend. Variation of Co hcp peaks significance may due Cr or Pt atom substitution of Co atoms in the Co-rich grain cores. Combined with the analysis of Co-rich grain size by X-ray diffraction peak broaden width, which was not very consistent with the result obtained from other's TEM and AFM studies, Cr diffusion was suggested to be the governing factor at short annealing time region. Co-rich grain growth should also be applied to explain the variation of magnetic properties in longer post annealing.