Abstract: The hydraulic cylinder, the executive part of the hydraulic system, appears oil leakage fault in the long-term use process. Through the sealing principle analysis, sealing structure analysis, finite element simulation analysis of the O-shaped rubber sealing ring, low temperature test verification and other ways, the reason of oil leakage failure of the static sealing structure is obtained. And according to the reason of seal failure, the solution measures are studied. The results show that the compression rate of the O-ring static seal structure of the hydraulic system will decrease at low temperature, resulting in sealing failure. By increasing the cross section diameter of the O-ring, the compression rate at low temperature can be effectively improved, thus improving the oil leakage fault., to provide reference for the leakage fault of the same type of products..