Abstract: Some researches shows that because of“de－couple”phenomena，skull－melting method was not able to keep the stable melting state of sapphire for long time.The melting sapphire tended to slowly de－couple，which weakens the coupling between the melting sapphire and the electromagnetic field，and then the melting sapphire freezes spontaneously in 3 to 4 hours which destroys normal directional crystallization.So，this paper analyzed the possible causes of“de－couple”and made some improvement in this field of study.The author got the sapphire crystal in cm－level for the first time with the skull－melting directional crystallization method.Parameters of skull－melting method are as follows：RF power frequency is 0.8—1.8MHz，RF output power is 100kW，inner diameter of cold crucible is 200mm and drop speed of cold crucible is 3—10mm/h.Compared with the cubic zirconia(CZ)crystal grown by skull－melting method，the materials，produced with skull－melting method，can be divided into two groups：one is“conductor”with low resistivity(the level of 1—0.1Ω·cm)before and after melting；another is dielectric with high resistivity(the level of 10⁴Ω·cm)before melting which then turned into“conductor”with low resistivity(the level of 0.1 Ω·cm)after melting.These two groups of materials have a lot of different crystal growth characteristics worthy of doing further researches.