Abstract: The effective control of noise and vibration in astructural acoustic system depends largely on the accurate evaluation of thesound-structure interaction which is characterized by the energytransferring back and forth between the acoustic field and the structure.When the fluid is heavy enough, both of the responses of the sound field andthe structure can be significantly affected by this sound-structureinteraction. Applications of interest include acoustic radiation andscattering from a submerged elastic structure, acoustic cavity analysis, anddynamics of fluid-filled elastic pipe systems.In this paper, the cracked 2D elastic structure sound interaction problemsare studied by employing fractal two level finite element method combinedwith boundary element method. The cracked elastic structure is discretizedby fractal two level finite element method, which is divided into two partsby an artificial boundary. The crack neighbouring domain is discretized bythe fractal finite element method, which can reduced the freedom degreesgreatly through transforming the nodal displacements to a set of generalizedcoordinates, the another domain is discretized by the conventional finiteelement method. The exterior acoustic field is calculated by boundaryelement method, which satisfies automatically Sommerfeld's radiationcondition.In the numerical simulation procedure, the radiation and scatteringacoustical pressure by an infinite long cracked aluminum cylinder immersedin fluid are calculated, the results show that the resonate frequencies ofthe structural-acoustic coupled system become lower with the depth of thecrack increase, and that the effect on the acoustical field by the crack isparticularly pronounced in vicinity of the crack tip.