The characterizations of CdZnTe substrate and HgCdTe epilayer grown by liquid phase epitaxy have been carried out by means of infrared microscope, X-ray double crystal rocking curve method and X-ray topographymethod of precip itate , substructure and compositional segregation etc. The results show that dislocations gathered at the subgrain boundary in CdZnTe substrate expend to the ep ilayer HgCdTe in a radiation like way, resulting in the subgrain in epilayer and the larger lattice distortion stress area caused by defects, which affects the structural perfection in HgCdTe thin film.