In order to study the aging condition of composite insulator under different conditions

Fourier transform infrared spectroscopy（FTIR）and hardness testing method are used to analyze the aging conditions of samples operating different years and in the different positions from the same manufacturer.Meanwhile

the electric field distributions of composite insulators with different voltage levels are simulated.The hardness results show that the hardness of the upper and lower shed surfaces are increased with the voltage level

while the surface hardness of the shed in the middle part decreases with the voltage level.It is found that the hardness of the upper and lower shed surface with the same voltage level increased with the service life.FTIR test shows that the absorption peak of Si-O-Si decreased with the service life

the lower surface sample doesn’t show a clear regularity.The FTIR infrared spectrum characteristic peaks of the Si-O-Si and Si-CH3 functional group decreases with the increase of electric field strength of the silicone rubber composite insulator shed.For the composite insulators with different phases show that the absorption peak of the B-phase shed had the lowest degree of decrease

which indicates that the aging of B phase is the lightest than that of A and C phase.