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The composite insulators are widely used in power system, because of its remarkable performance on pollution prevention. In this paper, some 500kv insulators with different working time and manufactory are tested on their hydrophobicity, electrical character, mechanical character and aging character of the shed's material. The experimental results show that the hydrophobicity of composite insulators used this area degrades fast. The value of hydrophobicity of composite insulators is HC2-HC5 at the working age of 3 years, the HC5-HC6 at the 6 years, HC4-HC6 at the 9 years. And the samples also showed the bad performance on transfer, loss and recovery of hydrophobicity. It was found that the high temperature and humidity of environment was the main reason causing the decline of hydrophobicity. However the electrical and mechanical character of these old composite insulators still can meet the request of some regulations. The samples can resist the voltage of power frequency and lighting pulse respectively, and the destructive mechanical values are greater than the rated mechanical intensity. With the increase of the using time, the tensile strength, tearing strength and electrical erosion resistance strength of the sheds become worse. These operation characteristics are the good reference for the operation of power grid.