The HgCdTe layers were grown by Terich liquid phase epitaxy in a horizontal slider system. The relationship among the lattice mismatching of HgCdTe/CdZnTe, the Xray topography and the detectivity(D*) of the IRFPA was studied. For HgCdTe layer of Xray diffraction topography,we will classify it roughly into five categories: Crosshatch pattern, mixing pattern, uniform background pattern, mosaic pattern as well as by the quality of the substrateinduced ravine topography, the Crosshatch pattern and the mixing pattem materials prepared for IRFPA have higher detectivity on average. The results of Xray diffraction show that when the lattice matching of HgCdTe/CdZnTe about 0.03% ,the Crosshatch pattern appears clearly;When the lattice matching of HgCdTe/CdZnTe reduced, the Crosshatch pattern become into mixing pattern, uniform background pattern gradually and when the epilayer lattice parameter is smaller than that of the substrate(negative mismatch),the Crosshatch changes into a Mosaic structure. Therefore, for the specific cutoff wavelength devices, if we want to enhance the detectivity of the IRFPA, we can control the lattice matching of HgCdTe/CdZnTe in order to grown the epitaxy materials of meeting our requirements.