Growth method of large-size square sapphire crystal

The invention relates to a growth method of large-size square sapphire crystal. The maximal side length of the crystal is 320*320mm; 99.999wt% high-purity aluminium oxide is adopted and is put in a tungsten crucible; a tungsten heater and a tungsten-molybdenum thermal insulation material are arranged; the tungsten-molybdenum thermal insulation material is square; the heater is square; and the crucible is square. According to the square sapphire crystal ingot, formed by the method disclosed by the invention, the utilization rate of materials is increased, for example, a square crystal rod for a screen of an iPhone 5S model is hollowed out from 100Kg of sapphire crystal ingot; the utilization rate of the materials can reach 60%-70%; and the production cost is reduced by 20%-30%.