High-quality, large-size CaF2 crystals are urgently needed for advanced applications such as deep ultraviolet lithography and aerospace cameras. However, growing such crystals is a challenging task in the field of crystal growth. Heat transfer, flow, and phase change processes of 3, 7, and 20 inch (1 inch = 2. 54 cm) CaF2 crystals at different growth stages on the vertical Bridgman growth were conducted by numerical simulation. The results show that as the crystal size increases, the melt flow strength and the area of heat dissipation on the crucible wall increase, resulting in problems such as local depression of the melt-crystal interface, increase in the radial temperature difference, reversal of the temperature difference between the crystal edge and center, and decrease in the axial temperature gradient near the melt-crystal interface. Furthermore, this article discusses optimization strategies for growth rate and power of heater in the growth of large-size CaF2 crystals.