The bolted connection between DN300 valve flange and class2500 blind plate was taken as research object. The finite element model of the flange-blind plate bolt connection was established based on ANSYS software. The difference in axial displacement between the bolt joint and the middle of the adjacent two bolts were simulated under the coupling action of flange bolt preload and fluid pressure. The contact stress and axial deformation were analyzed in the sealing area when the preload was applied to flange-blind plate bolts based on the GB150 algorithm. The sealing performance of the circumferential direction of the flange was analyzed meanwhile and the experiment was conducted to verify the sealing performance. The results show that the circumferential sealing is better and the results of the experiment and simulation are consistent;the lowest limit of the bolts preload is determined; the contact stress of the outer ring of the sealing gasket is bigger than the inner ring, and the outer ring of sealing gasket plays the main sealing role.