In this paper, an alternative alloy of GH4080A for fastener application in the steam turbine running at the parameter near 630℃ was considered. And notch stress rupture tests under different loads processed under the same heat treatments and melted from Special Metals Corporation and Fushun Special Metals Company, respectively. Then, the relationship between characteristics of microstructure near facture zone and the dispersivity of rupture life was systematically investigated by using OM, SEM and EBSD analysis. The results are as follows: the difference of rupture life for specimens melted from Fushun special metals was mainly due to the different grain size distribution at egde and at the center of the billet bar. While the reason that the difference of rupture life for spicimens at the billet bar edge melted from Fushun special metals and Special Metals Corporation was based on the different deformation mechanisms under rupture loads, and grain boundary sliding was the dominant deformation for specimens melted from Fushun, the grain boundary sliding coordinates with intracrystalline plastic deformation for specimens melted form Special Metals Corporation.