Magnesium oxide single crystal is made from high purity magnesium oxide, which is produced in the process of producing high-purity fused magnesite with an MgO content of more than 99.90% and a volume density of more than 3.5g/cm3. Magnesium oxide single crystal is transparent crystal that have extremely strong resistance to high and low temperature(high temperature 2500℃, low temperature -270℃) corrosion resistance, insulation, good thermal conductivity and optical properties of colorless, widely used in production of ferroelectric thin films, magnetic thin films, optical thin film and high temperature superconducting thin film etc.