Abstract: There is the coolant with radiation, high temperature and high pressure in the reactor pressure vessel（RPV）. It is closely correlated to RPV sealing capability whether the whole nuclear system work well or not. The aim of this paper is to study the seal analysis method and technology, such as the pre-tensioning of the bolt, elastoplastic contact and coupled technology of thermal and structure. The 3D elastoplastic seal analysis method really and generally consider the loads and model the contact problem with friction between the contact plates. This method is easier than the specialized seal program and used widely.And it is more really than the 2D seal analysis method. This 3D elastoplastic seal analysis method has been successfully used in the design and analysis of RPV.