Through establishing three dimensional finite element analysis(FEA) model of the structure of nonstandard doublecone ring used for the flat cover and cylinder seals of a hydrogenation reaction chamber,the stress distribution on seal faces of gasket in both preloading and working condition were studied,and the seal condition of the nonstandard doublecone ring was discussed.The relation of radial gap with pressure and stress of gasket was also studied.The results show that the nonstandard doublecone ring can achieve original seal in preloading condition,and provide good seal property in working condition.The seal pressure ratio and stress of the gasket are increased along with increasing of radial gap,and this nonstandard doublecone ring seal can achieve good sealing in the range of radial gap given according to standard GB1502011.