The damage mechanism of a diaphragm accumulator was studied. The deformation of the diaphragm with different compression ratios were calculated using ANSYS software. The friction collision between the diaphragm and the support ring was analyzed. The friction test rig of diaphragm accumulator was built, moreover, the deformation and friction of the diaphragm were studied experimentally in different conditions, the results further validated the numerical results. This study shows that the failure of the accumulator is mainly caused by the friction collision between the diaphragm and the support ring when the compression ration exceeds the permitted value.