In order to investigate the meshing scale of the FE-IE (finite element coupled infinite element) method for a ring stiffened cylindrical shell, the guidance was put forward for the structural wetted surface. Numerical results show that, for ring-stiffened cylindrical shells, the bending wavelength of the main vibration mode can be taken as the reference of meshing scale in FE-IE calculation which is testified with at least two finite elements per distance of stiffeners. There are at least six finite elements per one bending wavelength of the main vibration mode. The bending wavelength of the main vibration mode is used as the reference of meshing scale of FE-IE calculation rather than the shortest wavelength of structural waves. The obtained conclusions are significant to the meshing of structural wetted surface and the controlling of the total number of elements in the interior fluid region.