NaI (Tl) scintillators are widely used because of their characteristics of high detection efficiency, good temporal characteristics, and minimal temperature influence. In order to meet the needs of nuclear radiation detectors with high detection efficiency, large size and high energy resolution NaI (Tl) scintillators are required. Based on the growth characteristics of NaI (Tl) crystals, the main furnace body, temperature field system, crucible, heating power supply and other components of the large size NaI (Tl) growth crystallization furnace were studied and designed. In conjunction with the control system of the large size NaI (Tl) growth crystallization furnace, innovative fusion method was used to grow NaI (Tl) scintillator materials with a diameter exceeding 300 mm, which provides direction and solutions for the subsequent growth of large size NaI (Tl) crystals in China.