Post annealing treatment for CoCrPt magnetic thin films were tried in different thermal conditions, by changing the time of annealing procedure. Coercivity (Hc) improvement was achieved in annealed sample compared with those as deposited, in which as high as 5.2 kOe has been attained. To clarify the mechanism of annealing treatment on the magnetic properties, X-ray diffraction (XRD) spectrums of those samples and their 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 hexagonal structure increases monotonically with increased annealing time. Variation of Co hcp peaks significance may due to Cr or Pt redistribution in the crystal grains and its boundaries. Combined with the grain size analysis of Co-rich area 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.