Abstract: The flange-bolt is an important part of nuclear pressure vessel, and it acts an important role in normal operation of reactor. In the paper, the model, including closure head of reactor pressure vessel and secondary manway of steam generator, was equivalent simplified for axisymmetric analysis and 3D finite element contact analysis, and it was also compared for each other. The different ways were discussed and compared for accomplishing bolt pretension in the structure. The results obtained by axisymmetric model are correct and conservative.