Abstract: The silicone rubber (SR) composite insulator is the most widely used insulator in transmission lines, but its actual lifespan is only 10~20 years, which is far less than 50~100 years of the porcelain/glass insulators. Due to the risk of aging of composite insulators and the huge investment of replacement, the composite insulator used to control pollution flashover may become a serious problem for power grid in the near future. Therefore, greatly improving the lifespan of composite insulators is an urgent problem to be solved. The decay fracture and the degradation of anti pollution flashover performance are the two focuses affecting the lifespan of composite insulators. The statistics of operating composite insulators, calculation of electric field distribution, dissection of decay fracture insulators, bend-electricfield-temperature- humidity test and low temperature mechanical properties test of SR sheath show that the alternating bending is an important cause of cracked insulators. Under the combined effect of alternating bending and low temperature, it is easy to cause the deterioration and cracking of the sheath with low SR content, thus the protection effect on the core rod and interface may be lost, and a large percentage of decay fracture insulators may occur in the insulators that are easy to bear bending load, such as compact V-strings and jump strings. The excessively strict requirement for electric erosion of sheath is a technical mistake in the development of composite insulators, which has become a bottleneck to improve the lifespan of the composite insulator. Reasonably breaking through the electric erosion parameters of current standard to achieve a substantial increase in the SR content of sheath is the key to maximize the weather ability, cold resistance, low temperature elasticity of SR and improve the lifespan of the composite insulator.