Abstract: If threaded fasteners used in the reactor interior are of dissimilar-material, considerable additional stress may be induced when being heated due to thermal expansion coefficient difference between bolt material and flange material. In this paper, finite element model of typical dissimilar-material threaded fastener M12 was built and analyzed by simulating cyclic thermal load conditions in the reactor interior. Varieties of parameters, such as deflections of the bolt and flange, stresses under various preloads, heating, and cooling conditions, were researched to provide reliable basis for engineering design.