The head machine is in the underground for a long time, facing intense vibration , large side load and the gravel soil environment, the heat dissipation condition is poor, plus the continuous work and poor maintenance. Once the boring machine breaks down, it will bring the big loss to the construction company, therefore the structure fatigue resistance of hydraulic cylinder, the impact resistance and corrosion resistance of the coating, and anti-pollution requirements on the sealing structure are very high.