In the operation of power system, insulator flashover is a common accident which has serious effect on high voltage transmission line. Some methods, such as cleaning contamination, creepage distance adjustment, using anti-flashover coating and using composite insulators, have been emerged with the development of anti-flashover technology. Among those methods, the composite insulators were widely used because of its excellent stain resistance characteristics. This paper reviews the mechanism of flash insulator pollution, measures of anti-flashover, structural characteristics and excellent performance of composite insulators. Finally, frequently asked questions in the course of its use were discussed.