The sealing performances of the bolted flange joints with double tapered gasket and octagonal gasket were analyzed by finite element software of ABAQUS. The maximum stress between flange and bolt,the maximum contact pressure on each sealing surface and the effective sealing width between two gasket were analyzed and compared under working conditions and operating conditions. The results show that the internal pressure makes the maximum stress of the flange with double tapered gasket drop, but its stress of flange and bolt is still higher than that of the flange with octagonal gasket. With the increasing of nominal diameter, the effective sealing width of the inside and outside surfaces of octagonal gasket is decreased, but the double tapered gasket shows an increasing trend in the effective sealing width of the master and slave surfaces. The special wedge structure of double tapered gasket makes the decreasing amplitude of contact stress less than the octagonal gasket under internal pressure, therefore double tapered gasket has good sealing performance, especially for the sealing of the flange joints with large nominal diameter.