In order to further reduce the procurement cost, improve the maintainability of the equipment and break the monopoly of foreign countries, the detection performance of the domestic large-size NaI (Tl) detector is improved by optimizing the packaging coupling mode of the crystal. The resolution and short-term stability of the whole body counter system equipped with domestic and imported large-size NaI (Tl) detectors were tested and compared. The experimental results show that the energy resolution of the homemade large-size NaI (Tl) detector is less than 8%, and the peak position variation is within ± 1%, which can meet the measurement requirements.