In order to study the sealing resistance characteristics of the O-ring in water medium,the 2D axisymmetric finite element model of the O-ring was established in ANSYS,the influence of different pre-compression rate and fluid pressure on the sealing performance of the O-ring was analyzed,and the friction of the O-ring under different fluid pressures was calculated through two sliding friction theory algorithms,it was compared and analyzed with friction measured by the experiment.The effect of fluid pressure and reciprocating speed on friction and friction factor was explored.The results show that as the pre-compression ratio increases,the stress and contact length of the O-ring von Mises increase;with the increase of fluid pressure,the von Mises stress of O-ring increases,the contact pressure and contact length increase accordingly;when the fluid pressure is exceeded 30 MPa,the contact length decreases;the friction obtained by the micro element method is close to the experimental value,can be used for O-ring friction estimation;at the same reciprocating speed,as the fluid pressure increases,the friction of O-ring increases;with the same fluid pressure,the friction also increases as the reciprocating speed increases.