The model of O-ring for slurry shield machine was established by using ANSYS software to analyze the variation of contact stress with compression ratio,fluid pressure,friction coefficient and hardness.The function relation of contact stress with compression ratio and fluid pressure was fitted.The results show that the main contact stress,VonMises stress and shear stress are increased with the increasing of hardness,compression rate,fluid pressure and friction coefficient.However,the friction coefficient has little effect on the stress of O-ring as a whole.The higher the hardness of O-ring,the larger the variation rate of stress with compression rate.When the fluid pressure is small,O-ring with low hardness should be selected,so that VonMises stress and shear stress are both lower and the probability of crack and shear failure of the O-ring is reduced.When the fluid pressure is large,O-ring with high hardness should be selected to ensure that the main contact stress is larger than the fluid pressure.Contact stress is direct proportion relation to the fluid pressure and the proper compression rate under different fluid pressures could be calculated by the fitting formula of contact stress,compression rate and fluid pressure.