Abstract: The vibration characteristic and radiated noise from the motorcycle engine shell are analyzed with Finite Element Method / Boundary Element Method,including mode analysis,frequency response analysis and simulation analysis of the structure's radiated noise by the original engine shell,and the experiment on this shell has been done.The experimental data are close to the theoretical data,so the FEM/BEM seemed to be a good way to predict the radiated noise.Two methods of improving shell's characteristics,i.e.changing shell's rigidity and shape respectively,are proposed based on the theoretical data.The new shells are also analyzed with FEM/BEM,and the results indicate that both of them are the effective way to restrain the radiated noise.Moreover,the experiments conducted on the improved shells confirm the reduction of the radiated noise.