In order to meet the development needs of solid-state lasers, it is necessary to continuously improve the YAG laser crystal growth technology. However, controlling the defect structure in YAG is particularly important for crystal development in industry and scientific research. The defects of crystal samples prepared by the two processes were studied, especially the origin of crystal scattering points. Positron annihilation technology (PAT) is a sensitive and effective nuclear technology analysis and characterization method for the microstructure of materials, which is extremely sensitive to vacancy defects and micropores. According to the analysis results of positron annihilation technology including positron annihilation lifetime spectrum and Doppler broadening spectrum, the positron lifetimes and line-shape parameters of Doppler broadening spectra of samples with different processes and with or without scattering points are different, indicating that the main defects of the crystal are