Abstract: The characters of sapphire, especially its birefringence, are investigated. The antireflection films(AR) on sapphire are designed and prepared. The film's properties, such as wavefront, morphology, are measured and analyzed. A laser heat distortion experiment is carried out, and the variation of wavefront of coated sapphire and quartz are detected. A damage threshold of at least 10kW/cm2 is determined of the coated sapphire.