Abstract: An elastic-plastic nonlinear analysis is conducted by ABAQUS software to study the sealing structure of flange connection with different material in horizontal channel. The processes for pretightening of primary bolts and pressurizing in the horizontal channel are simulated by finite element multi-step skill. The stress distribution and sealing performance of primary flange is studied. The analysis results show that the double O-ring sealing structure in horizontal channel can meet the requirements on strength and sealing dur-ing the pre-tightening and pressurizing processes.