High purity germanium detectors have the advantages of high resolution, high detection efficiency and strong stability, and their applications are becoming increasingly widespread. However, the preparation of ultra high purity germanium single crystals, the key materials for high purity germanium detectors, is challenging due to the high purity and high quality requirements. The domestic technology for preparing ultra high purity germanium single crystals is still immature, and the quality of the prepared crystals is still not high enough. In this work, large size ultra high purity germanium single crystals were grown in hydrogen atmosphere using the Czochralski method and self-made equipment. The crystal properties were analyzed through low-temperature Hall measurement, dislocation measurement, and deep level impurity measurement. The results show that the net carrier concentration of the as-grown germanium crystals is less than 1×10¹⁰ cm^-3, the deep level impurity concentration is less than 4.5×10⁹ cm^-3, the dislocation density is less than 5 000 cm^-2, and the number of dislocation array is less than 3, which meet the requirements of ultra high purity germanium detectors. Finally, qualified crystals with a diameter of 85 mm and a length of 60 mm were obtained.