Abstract: In order to investigate the effects on the underwater radiated noise of a stiffened cylindrical shell due to welded defect,a stiffened cylindrical shell with welded defects was studied via finite element method coupled with boundary element method.The underwater radiated noise of the structure with different lengths,angles,positions of defect and numbers of rib containing defects was calculated,and the frequency response function of radiated noise was obtained.The comparison and analysis of the results show that the lengths,angles,position of defects and number of ribs containing defects have effects on underwater radiated noise.Generally,the effects of defected rib nearer the bulkhead on the radiated noise are less.According to different lengths,angles,position of defects and number of defected ribs,a comprehensive analysis on the structural radiated noise can be carried out in the engineering application.The results can be used to analyze the radiated noise measurement of submarine.