Nd:GGG crystal with large size and good optical quality is required to applied for solid-state heat capacity laser (SSHCL), and the major way to obtain the crystals is to grow with flat interface by the method of Czochralski. In this paper large-sized Nd:GGG crystal of 75 mm diameter and 60 mm length is successfully grown by the flat interface growth technique in the furnace equipped with automatic diameter control appliance. And the crystal is absent of scattering particles and shows good optical homogeneity.