The structure and photoelectric properties of ZnO single crystal grown by homoepitaxy before and after annealing was reported. The red-brown ZnO single crystals were grown by the chemical vapor transport (CVT) method. The ZnO single crystal annealed in a high-temperature oxygen atmosphere shows colorless and transparent. The structure of the ZnO single crystal before and after annealing was analyzed by XRD, XPS, EDS, and Raman. The effect of annealing on the defect type and structure of a single crystal was discussed. XRD results show that the growth direction of the ZnO single crystal is (002). The FWHM of ω-rocking curve of ZnO single crystal before and after annealing is 59″ and 31″, respectively. It indicates that the defects in the single crystal decrease significantly after annealing. The composition and valence of elements in the single crystal before and after annealing were analyzed by XPS and EDS, and the results show that the content ratio of Zn and O elements in the single crystal after high-temperature oxygen atmosphere treatment is closer to the theoretical value. Raman spectroscopy analyzed the high-temperature oxygen atmosphere. The different Raman vibration modes of ZnO single crystal before and after annealing were analyzed. Through UV spectrum data analysis, the optical band-gap of ZnO single crystal before and after annealing is obtained to be 3.05 eV and 3.2 eV, respectively. Finally, the ZnO single crystal’s electrical properties before and after annealing in a high-temperature oxygen atmosphere were analyzed by Hall test. The low-temperature electrical transport characteristics of ZnO single crystal before and after annealing were discussed in depth.