Abstract: Radiated sound pressure of an infinite periodic ring-stiffened cylindrical shell in fluid field was studied by both theoretical and experimental method. The harmonic motion of the shell and the pressure field in the fluid were described by Flügge shell equations and Helmhohz equation respectively, and four kinds of rings＇forces and moments were considered. The responses of the shell were deduced by using periodic theory, and the radiated sound pressure could be obtained by utilizing the coupling boundary conditions. And the results were compared with those obtained from experiment.