Based on patterned sapphire substrate (PSS) technique, threading dislocations density (TD) in GaN epilayer can be reduced and the internal quantum efficiency (IQE) as well as light extraction efficiency (LEE) of light emitting diode (LED) can be improved. Highly efficient LED based on GaN can be grown on patterned sapphire substrate. A review of PSS technique is given based on published papers, including the development of PSS technique, its fabrication and pattern structure, process of GaN epilayer growth and performance improvement of LED on PSS. IQE and LEE can both be improved by PSS, but it is unknown that improvement from IQE or LEE achieved by PSS is essential. The mechanism of improvement of IQE and LEE is not very clear, while arguments about the mechanism proposed by published papers are given. The effects of different PSS structures and sizes on the quality of GaN and performance of LED are not well investigated yet.