By e-beam evaporation, the passivant ZnTe has been deposited onto the CdTe surface that is treated by suitable etching solution to prepare a better surface condition for the deposition. The structural variations and the optical properties of the interface layer of ZnTe:CdTe heterostructure according to the condition of pre-heating and thermal annealing have been studied by photoluminescence (PL) and X-ray diffraction (XRD) measurements. The PL result reveals that the deep-level donor acceptor pair (DAP) emission related to the concentration of acceptor centers (isolated cadmium vacancies: V-Cd) responsible for interface trap states (Te4+) is reduced by thermal annealing. From XRD results, it is shown that the polycrystal layer of ZnTe is transformed to the polycrystal layer of CdZnTe by the thermal annealing process. By Auger electron spectroscopy (AES), the relative composition and the interface structure of ZnTe/CdTe after thermal annealing are analyzed. It is indicated that the CdZnTe layer is formed by interdiffusion process through the interface of ZnTe/CdTe.