The bolt,gasket and flange system of the main sealing interface of oilimmersed transformer was modeled by the finite element analysis software ABAQUS.The force and deformation of flange bolts under preload condition was analyzed,and the change rule of contact stress with compression ratio of rubber gasket,fluid pressure and hardness of rubber gasket was discussed.The results show that under the action of bolt pretightening load,the flange deflection causes uneven stress on the bolts,and the box along the joint is the most vulnerable position of the flange.Additional rigid fixation can be added at the box edge and box body to increase the strength.The maximum contact stress and von Mises stress are increased with the increasing of compression ratioand fluid pressure.Under the same fluid pressure,the greater the hardness of rubber gasket is,the greater the contact stress and von Mises stress are.Therefore,the rubber gasket with higher hardness should be selected when the sealing interface is under large fluid pressure.