The computer simulation of X-ray rocking curve is an important method for characterization for the semiconductor materials. The calculation of the intrinsic rocking curve is the foundation of its simulation. The intrinsic reflectivities of Hg1-xCdxTe and Cd1-zZnzTe materials are calculated by using X-ray dynamic theory and the effect of compositions and thicknesses on intrinsic reflectivities and full width at half maximum (FWHM) is studied. It is found that intrinsic reflectivities and FWHM of Hg1-xCdxTe and Cd1-zZnzTe materials depend on their compositions and thicknesses. The reflectivities and FWHM are determined by X-rays scattering and absorption in the materials. If the film thicknesses are smaller than penetration depth, the changes of the shape of the intrinsic rocking curves, intrinsic reflectivities and FWHM are also affected by theirs. If the thickness of Hg1-xCdxTe films is larger than 7 μm, the changes of the intrinisic reflectivities and FWHM of the (333) diffraction plane would be very small.